Any ppc version without dual graphics is going to halt you playing aga games, so you probably are looking for a multisync monitor as opposed to a fixed 60hz or higher.
And unless you already own the software to get it all running full registered versions will quickly put you past any limit you set, then theres the question of sound eeek !
scrap everything I,ve written so far look at http://vesalia.de
and check out their mediator to 1200 add on solutions
In short unless you spot a complete super miggy with all the trimings going really cheap I don,t think there,s a single best answer, really besides games what else are you using it for ?
allthough I hate to say it using a SPIT PC & emu IS the sub 300ukp way to do it .
Real migy will cost you more a lot MORE if using new add on's. :eek