Hi,
It's always cheaper to buy an integrated amp than separates, because an integrated uses one power supply (transformer, etc). Separates have to duplicate the power supplies and chassis, which increases the cost.
With modern solid-state (transistor) electronics, virtually any competently designed amp will "pair well" with the M22ti speakers. The M22ti is an 8-ohm speaker, so current-flow and overheating at low impedances (4 ohms and lower) isn't an issue.
Audiogon is a good source for used gear. With reliable brands of amps (NOT vacuum-tube gear), nothing really deteriorates for 10 to 15 years, so as long as the amp hasn't been abused, you should be okay.There are brands that at various times have had quality-control and reliability problems in the past (Carver being one such) but it's easier for me to tell you brands of electronics that in my experience have been very reliable over the long term. Here are some, by no means all, that come to mind: Bryston, Yamaha, Denon, Pioneer, Rotel, older Onkyo separates and receivers.
Regards,
