If you buy a solid working game, financial parts costs should be pretty low, but if you are new you will likely spend some time and effort on diagnosis and repair time.

That said, depending on what you already have at home there are some tools you'll want to have that will obviously cost money (multimeter with continuity tone, soldering iron, and "general" tools such as screwdrivers, socket set, wire strippers, etc.).

Like everyone else has said, there will at a bare minimum be basic adjustments and repairs like a switch needed realigned, wire came loose, etc. as you are launching a metal ball into plastic, mechanical, and electrical parts...that's just the cost of doing business .

I dont think most people (myself included) knew much if anything about maintenance and repair but there are so many resources out there that if you have the willingness and desire to learn, you'll be comfortable and on helping others in no time. I was scared to even change a bulb when I got my first game 3 years ago and last year I finished putting a Taxi back together that was literally in boxes and had 3 partially working MPUs that I needed to combine into one. If you are willing to learn you'll be just fine. Patience is key!