I love Catham Co! I've definitely got some folks in mind that might be willing to help out.
But one of the issues I see is that playing as a band into a single mic really takes some practice. So at our practices we need to be constantly practice distance control and movement etc. and be able to listen to the recordings to get feedback on what's working and not working. Plus while I would rather have someone help handle this, coordinating 6 piece band plus someone doing the recording for free (even in exchange for tickets and beer) is a lot of logistics. I'd like to have my own gear so I can just do it without having to coordinate with someone.
Anyway I think I'll pursue both avenues, find someone to help learn the ropes and get my own gear so I can have the flexibility. Suggestions on recording devices?
That practice seems very useful. It seems a little more difficult in bluegrass where the single mic is involved and the players essentially have to hold the circle. Nevertheless that may (or may not) be how you'd find you band mic'd at larger performances/broadcasts/professional opportunities so were it me I'd have a goal of being good at the control required...
Coordinating the band plus the recording seems a bigger challenge than having someone else do it but I think you would need your own setup if you want to do every show and rehearsals and all the rest.
Your budget seemed pretty limited as well I think (though you at least have a solid single LD mic). The onboard mics of a device are usually pretty limited but if it is close and you're not loud they may provide something useful.
As to recorder that Tascam does seem to be sort of a least cost 4 channel set up. There is likely a lot of discussion of it around here in other threads.
Given all that's on your plate I'd keep it simple. Any of the ideas above are good. You could start with the LD and onboard and see if that gets you something useful. If it does good. If not or if you want further improvement you can add other mics. 4 mics would likely cover most scenarios. It is out of your price range but DPA offers a really nice clip on instrument mic for upright bass. IMO that is the best approach to that instrument. A lot of professionals use this and if they can get a DI for the bass in larger settings will ask that be used.