So you've got an idea for a side project or something that you'd like to start. When you inevitable find out that it's already been done. Do you quit? Do you continue. How do you feel?
I usually feel discouraged. Should I? Should you stick with it, and try to put your mark on it.
Edit: actually, that's a little too glib. Let me say this instead "just do it different". And that's actually not a glib answer, because I mean something very specific by that. In almost every market, there are always multiple vectors along which you can differentiate your offering. To grossly over-simplify, you could optimize on "price", "quality", "customer intimacy", etc.
For example: if there's a company out there offering something like your thing, but offering it very cheap, then don't try to be the "low bid" vendor. Instead, become the "boutique" or "luxury" vendor that sells to customers who want white-glove service and are willing to pay for it. OR, do the opposite... if your erstwhile competitor has what appears to be very high prices, see if you can build your thing in such a way that you can sell it much more cheaply. Note that in either of these cases, your not necessarily competing for the same set of customers! There may be some overlap, but there are always customer who want "the cheapest", or customers who want "the best", or customers who want the whole "white glove treatment" thing, etc.
Also, as an aside, be wary of trying to compete for "lowest price" as this can lead to a "race to the bottom" situation and make it very hard to maintain any kind of margin. If you want to lower prices, do it by finding a way to operate more efficiently, instead of just sacrificing margin, if at all possible.
There are a few variations on this theme, and you could argue there are a lot of variations depending on how fine-grained you get in terms of how you segment those "vectors of differentiation". To learn more about this overall concept, I highly recommend reading The Discipline of Market Leaders by by Michael Treacy and Fred Wiersema.