is it wise to replace the ecm

i'm not a dodge owner. but i may be soon. theres a 2001 dodge neon for sale. and the owners claims that the only problem, is the need for another computer. would that be a wise investment? i was thinking that i'd go to a junkyard, spend 30 bucks, and try it out on the dodge. how easy is it to get the ecm to work. anything special that i'll need to do. also are dodge neon keys magentic,will they need reprogramming if i switch ecms

Automatic or stick trans has diffrent ecm HO engine is driffrent, not sure about what other years will fit.