I also play using IEMs, and for me using two directional condenser mics for the room works very well, especially combined with a couple of mics used as drum overheads. This also allows me to control (to a certain degree) the volume of myself and the rest of the band.
Although I haven't tried using an omni in the room, I suspect that the balance would be off, and that I would hear too much drums compared to the rest of the band. But this will vary depend on musical style, the ability to hold the volume down for the whole band and personal preference.
As for mic choice, any cheap condenser will usually work; I've used a couple of Samson C02 which worked okay enough for practice, pairs are for sale with stands and cables for ~$150 on Amazon.
If you plan on using the mics live I'd do as in the other answer; spend a bit more and get better mics. Ideally, see what other people in the area use and see if you can try them out. Personally I tend to go with Røde NT3 when I'm playing myself, but as a sound tech I tend to end up with AKG P170, Sennheiser E614, AKG C214, or Shure SM81 depending on availability and budget.