A decent 20" long arm machine will cost $3000. A decent 30" long arm will be $4500. For the number of times you are going to need a long arm machine, it's not worth it.
Any Juki 1541 will work fine. You don't need automatic back tack or automatic thread cutting, you just need a basic lockstitch machine with compound feed, walking foot(alternating presser feet is the correct term), and reverse. Anything more than that is overkill.
No one lives forever, the trick is creating something that will.