More than money, a clear STR (steps to reproduce) would be the most helpful, as having a clear STR saves a TON of time.
So the STR should be as close as possible to 100% always working.
e.g. (I'm just making this stuff up because I don't know what the STR is and I don't even know if Samurai Warriors has 2 discs, but let's say it does, so someone who can actually reproduce the bug should create the STR):
0. Run PCSX2.
1. Select the ISO of Samurai Warriors PAL (SCES 12345) - DISC 1.
2. Mount this memory card (and attach a minimal memory card to test with).
3. Boot fast.
4. From the game's menu: load game, then choose the save on the memory card.
5. Do (some steps) and the game will ask you to put in DISC 2.
6. Here I tried blah blah, and blih blih, and hoo-ha.. and nothing works. How do I make it recognize disc 2??
So, a working and reliable STR which the devs can follow and reproduce the problem is much more helpful than $20, because it saves them a lot of time which is worth way more than $20
And also, devs actually like to fix stuff, but ONLY if they can actually see that it's broken, and for that to happen they need a great STR.