Cheap? Mtb suspension, nahhhh.
You can get a air can seal kit to do it yourself, which may cure the oil leak, but probably won’t cure you propedal issues. Also a ‘proper’ service will include re-pressurizing the nitrogeon charge, something it extremely doubtful your LBS will be able to do (IME even motorcycle shops with the proper kit don’t want to do this for you).
If there no wear marks on the shaft, then get it serviced, it’s a great shock. I’ve yet to be convinced that any other air shock is as good (new RS stuff looks good but no long term tests yet)
Loco and J-Tech are coming through as two cheaper options that the main players (TF Tuned/Mojo)