Servos can be cheap, in comparison the the other stuff: Futaba S3004s work great for these size warbirds, and are less than $15 each. Lot's of other affordable choices too.

Mechanical retracts are less expensive, and no less reliable if installed correctly. I like to use independatnt, hi torq, low profile servos for the retracts, which can be adjusted for speed so that they retract slowly, AND at different speeds (VERY realistic looking).

Maybe once you get things around: you coukld start a 'build thread', we all benefit from such thread. US by learning from your mistakes (IF you make any) and you by being able to tap us for advice, based on OUR mistakes.