A decent stereo amp will work, yeah. Not ideal, but chances are you wont be able to tell the difference (unless you have real crap). It is best if your amp has a bypass button, which bypasses the EQ, loudness, DSP and any other 'features.' You dont want to use any of that crap when monitoring, they degrade the sound quality and confuse you. Hell, you dont want to use any of that crap when listining either... but thats another topic.
Event has a monitor that can be had at guitar center for $299, I think these are great speakers. Is there a guitar center near you? If not, a lot of places online offer free shipping on gear (provided you spend enough $$$) but your not going to find what your looking for at best buy. They only sell Crap.
So Look at (or better, listen to) the event 20/20s passives, or the Yorkville YSM1i (Which go for $200 I think). If you got more $$$ we can talk bigger / better... but the 2 I mentioned will do the job. (actually I never heard the yorkies... but they get praised a lot on this forum, and are cheap)
I use a $400 pair of B&W audiophile bookshelf speakers. Some guys will knock me for that, but I think they are awesome... flat, neutral, accurate and they sound good too... A lot of people seem to imply a monitor has to sound like crap to be any good (I think thats BS, just needs to sound neutral).
thank god we all have a right to our opinion.