If you are using a mic, you already have a preamp, but maybe not so good. mixers have preamps, some stand-alone recorders have preamps, and some sound cards have preamps. Most studios use a mixer for a bunch of cheap preamps, and a few dedicated channels of high quality pres for critical tracks, such as vocals and acoustic instruments.
Are they affordable? that's debatable. This is an area where more money usually = better sound. Mic pres run from $80 to $5000+ per channel!. The real answer is, in my opinion, that mic pres are the single most critical pieces of equipment in a studio, more important than the mics. What I mean is that a cheap well made mic like a Shure SM57 will sound great through a good preamp, but an expensive mic through a cheap pre will usually suck.
At assorted price points, check out these pres- M Audio Audio Buddy and DMP-3 (wicked cheap). Studio Products VTB-1 ($200 or so) FMR Audio RNP/ Grace Design 101/Joemeek VC1Qcs (all about $500 or so) If you don't know whether you need a preamp, the answer is yes, if you use a microphone for anything.-Richie
