+1 to @yoyoyaya comments. With just a $500 budget you aren’t going to get any "great" mics, however, as he noted you could get a Zoom H4n Pro or one of the similar new ones for about $200 to $250 with onboard mics and use them. If you bought condenser mics like the Rode NT5 ($429) or M5 ($200) you’d need a microphone preamp to give them phantom power. Microphone preamps can be $$$. I’m not aware of any "cheap" ones but B&H might point you to one. The advantage of the Zoom H4n Pro and similar recorders is they have XLR inputs and onboard "decent" preamps.
For recording concerts and posting them to the Internet Music Archive after doing some postproduction work on the files, I record with a Zoom H4n Pro but use external mics. I have the Rode NT5 stereo pair (which are generally fine) but usually use my nephew’s older but slightly more detailed bass response AKG-391 mics.
If I were younger and had the money, I’d pop for some Schoeps MK4 and a SoundDevices recorder with great onboard preamps.
Note that these Zoom and Tascam and Sony digital recorders can do a lot more functionality than just recording two-channel audio but don’t let that phase you. You won’t need to worry about all that "other stuff". Recording is fairly easy.
I see you got a Tascam X8. I suggest the $200/pair Rode M5 as a low-cost microphone solution that should be fine for your use case.
One "issue" I have with YouTube audio demos (other than it being lossy) is that the posters very rarely (if ever) state how loud they are driving the speakers, so you don’t know if they are played at low volumes (75dB) or are being pushed to higher, more stressful volumes (90dB and above) so it makes gaining any useful knowledge from the demo questionable. Have fun.