I love the market. Markets are amazing things.
Here's a simple question, and it really does boil down to this.
How much do YOU and your friend want?
No. Really.
It's your time, it's your life. Hours are the one thing you won't get back. What is it worth to YOU to do this project for THEM.
They, on the other hand, have an idea of how much they want or are able to pay for it.
If your price is below or equal to how much they value the project - then it's a win.
If not, and you're too high, then I guess you're either not getting the project or you're willing to sell your time for less than you think it's worth. So, was your valuation correct? Not what is THERE valuation of YOUR time, what is YOUR valuation of YOUR time.
The "Market Price" is what the market, at large, seems to be willing to pay or charge for things. But that really depends on your market, and who's in it, etc.
If you set your price fairly, to how you value your time, and they take it, then you have a fair deal, yes? You didn't get "ripped off" if you bid "too low", because it's your evaluation, fairly made. Right? And they won't be "ripped off" if it's too high for them, because they set a budget as well.
Regret over "I could have got X for less or I paid too much for Y", that's absurd. Barring getting raped by some mechanic in a remote desert outpost, you have the information you need for your time, and they have their budget, and their ROI numbers, etc. to make a fair judge of "what is it worth to them".
Different people value different things different ways. Maybe you value your time less because the project experience is more important than the time. Maybe they want this done when you planned your honeymoon -- cha ching! worth a bit more to you, isn't it?
So, make your price and go from there.