You don't need a nest egg of six or seven figures and a financial advisor to create a top-notch, diversified investment portfolio. For little or no cost, you can create your own portfolio using investment management alternatives such as free stock trading and free robo advisors along with low-cost exchange-traded funds.

In fact, in exchange for a small investment of time, you can invest and manage your own portfolio for only the cost of the underlying fund management fees, saving thousands of dollars over time. And you don't need to be an investing genius to do it.

"There are many resources available online to help you construct a globally diversified portfolio – usually consisting of various mutual funds or ETFs – similar to what you get from a robo advisor, but without the automated features," says Michael Ciccone, certified financial planner and associate vice president at Tradition Capital Management.

The key is keeping costs down because investment fees can eat into your returns. Consider, this example from the Securities and Exchange Commission: two investors, each with a $100,000 portfolio, earning 4 percent annually for the next 20 years, but one of those investors pays 1 percent for an actively traded mutual fund or a financial advisor, while the other pays 0.25 percent using ETFs or index funds . After 20 years, the second investor's low-cost portfolio would be worth $30,000 more for a total value of $210,000.

[See: 7 Investment Fees You Might Not Realize You're Paying .]

Depending on your investing sophistication, here are three ways to build your low-cost portfolio with varying degrees of help, from none for investors comfortable going it entirely alone to the option of getting some in-person answers to your money questions.

Do-it-yourself all the way. Cost-conscious individual stock pickers can't do better than paying zero commissions. With the Robinhood app, trading stocks is commission-free, and a desktop version is launching soon.

If you want a low-cost, copy-and-paste index fund portfolio, Paul B. Farrell of Marketwatch.com tracks eight simple diversified "Lazy Portfolios." They range from a three-fund Second Grader's Starter portfolio to the more complex eight-fund Aronson Family Taxable portfolio, and include each portfolio's return along with those of the individual funds. A DIY portfolio's only costs are the underlying ETF or index fund fees, which can range from 0.04 percent to 0.25 percent annually.

Each year DIY investors also need to rebalance , or buy and sell funds to return the portfolio to its preferred asset mix. For example, if your goal is 60 percent stocks and 40 percent bonds but after a year of stock market gains your mix is 70 percent stocks and 30 percent bonds, you sell 10 percent of your stock funds and buy bond funds with the proceeds.

A little help from a no-fee robo advisor. Not everyone is comfortable allocating and rebalancing a portfolio's assets. That's where no-fee robo advisors fit the bill. "Today's consumers expect a great experience that leverages technology to make the process easier – all at a great value," says Tobin McDaniel, Charles Schwab's senior vice president of digital advice and innovation.

[See: 7 Robo Advisors With a Human Touch .]

Several robo advisors offer rebalancing or asset allocation services as part of their free automated investing platform, among them M1 Finance . After you deposit money and build your portfolio with investments you select, M1 automatically invests the funds according to your plan, using fractional shares to put every last cent to work. There are no management fees or commissions, and you can choose from thousands of stocks and funds.

"M1 makes it simple, convenient and free to invest in what you want", says Brian Barnes, founder and CEO of M1 Finance. After you choose your asset allocation and investments, M1 rebalances the portfolio as well.

If you are unsure how to allocate assets and don't need access to thousands of investments, Ciccone suggests WiseBanyan. It makes asset allocation and rebalancing part of its free basic service and charges for "premium" add-ons such as tax-loss harvesting, which other robos include with their basic offerings.

Schwab's Intelligent Portfolios free robo advisor is even more all-inclusive. "It's the only robo-investing service that provides diversified portfolios that automatically rebalance and tax-loss harvest without charging any advisory fees, commissions or account services fees," says Schwab's McDaniel.

Schwab also holds the title of best performing robo advisor based on risk-adjusted returns over the past two years, according to Condor Capital's fourth-quarter 2017 edition of The Robo Report.

Occasional in-person guidance. But what if you need some in-person guidance or help with special portfolio management, tax or investment questions? Maybe you can't decide which type of account to open, or you're wondering how your year-end bonus will affect your taxes.

You can supplement free investment management or do-it-yourself investing with some targeted, paid professional advice. True, that advice will cost you if it's from an accountant or fee-only financial planner, but the time you'll need with a professional will be considerably less than if you relied on that person for all your investing needs.

[See: 8 Things to Consider When Choosing an Online Broker .]

In some cases and particularly if your question is investing-related, you may not need a paid professional at all. Charles Schwab and other discount brokers, such as TD Ameritrade and Fidelity, have financial consultants on staff to answer their customer's basic investing queries.

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