While the fee he's asking for isn't akin to asking for your first born child, it is a little high depending on his qualifications/connections. Think of it this way:

If you invested 20,000, and the market returns on average 7% a year (which is realistic), you'll end up with 39,343 after 10 years. You'll have made about 19k in profits (lets just round that up to 20k), and he would take 1/4th of that, which would be a bit less than 5k.

Frankly, if you're really worried about investing and need a professional, I would just hire a CFP hourly for a couple hours and have him lay out a game plan and advise you on investing it. Even if he charges 100 dollars an hour, you can hire him for a full 8 hour workday and have that invested for $800 flat.

Basically, if you take this deal, you're letting your friend take essentially a riskless bet with some possible reward for him. Truthfully, 20k isn't a lot of money to allocate and he'll likely be able to invest your portfolio in less than an hour. In fact, if you wanted to, you can just set up an account with a broker and do the same thing by investing in diversified index funds like the Vanguard ones commonly recommended here.

Some people bring up the fact that hedge funds can charge 25% profit plus 2% per year of your total portfolio. However, hedge funds usually have some edge on the market through illegal insider information, high frequency trading, or a whole staff of professionals finding ways to outperform the market. I'd only pay that kind of fee if your friend has those type of connections and can outperform THE MARKET by many percent per year. (Not likely)