Hippie gives some super excellent advise. (cept a hate using a 57 for bass hehe
akg d112 makes a great "cheap" bass mic , i got mine for $119 used)
What kind of gear are you using now?
Playing amplified, just like everything else in music takes some practice to get used to.
Playing without monitors can be a nightmare if the mains are too loud to let you hear your acoustic sound on stage. If you only have 2 speakers, Sometimes its better to run one main , one monitor than 2 mains depending on your gear and the size of the venue of coarse.... monitors bring the dreaded feedback into the equation, a nice 31 band eq can really help a ton with that though.
I personally think running sound for an all acoustic bluegrass band is about as hard as it gets. When your have 4-5 instrument mics and 2-3 vocal mics on stage things like ringing out the room become vitally important IMO.
Live sound is an art in its self, and you will always be limited by the gear you have available. Dont be discouraged though, its worth the effort and ultimately just as important as how well you play your instruments from the listeners POV.
I highly recommend the book "live sound reinforcement". It gets pretty technical but also covers the vital basics like ringing out a room and building a gain structure.
If you know a good soundman you can trust, dont hesitate to hire him or ask him for advise.
Also, Im a huge fan of in ear monitors, but they definitely take some getting used to as well.
Good luck to ya!