I am sure you can hit that thumb with a hammer too.
Anyway I know what you mean things tend to start small and grow into huge jobs, I found the same thing when renovating part of the parents home, what was going to be a $2000 relining and fixtures upgrade grew into $54000 of rewiring, new plumbing, insulation, metering boards and relining, it reached a point where I was starting to think the problems could only be fixed with a runaway bulldozer but it all worked out in the end and had fun doing it.
I would probably concentrate on stopping things deteriorating and fixing what can be done quickly while planning the bigger stuff for later, maybe it can be done with a few improvements.