My view on cost of maintenance for cycling, especially with MTBing and more so MTBing with FS bike - You need to learn some basic service skills - there are lots of resources online like University of U Tjoob and even on some OEM websites. Invest in some time and try them out yourself you will realise it isnt rocket science and will save you 1000's of ronds
So what should you be able to do yourself
Wheels - Fix a puncture; Change a tire; replace rim tape and gorilla snot; do a complete tjoobless conversion; True a bent wheel; Depending on which hubs you have you should be able to to service and replace hub bearings
Brakes - Replace brake shoes; re-cable brakes - A bit more advanced, but brake bleeding is not that hard.
Drive Train - Remove the cranks; remove and reisntall a BB; Measure wear on a chain; be able to break a chain to correct length; replace a chainring; replace a cassette; RD setting and tweaking; replace RD jocky wheels. Re-cable gears.
Suspension - Oil Service -I learnt this online and done it many times - Now i just send it off to RBC and pay them to do it, but i can do it myself if i have the time.
Bearing replacement - This is doable yourself, at most you will save on labor, but you will need to have the bearing puller tools for removal and reinstalling. I made my own from threaded rod and some different size washers, which work great. When i change bearings, i dont skimp i replace them all even the ones that still look okay.
As far as tools go - there are not that many that you would need to add to your toolbox
Bike service stand (this is a must) - Spoke wrench - Allen Key set - Torx set - tire levers - cable cutter - 15mm pedal spanner - Chain whip - chain break tool - chain wear gauge - Cassette tool - BB tool depending on your BB type - Valve core removal tool - shock pump (you should have gotten one with the bike) - big bottle of Stans - some syringes - proper grease, I'm sure some can add to these baisc tools needed
Over the years i've gotten more and more adventureous and made a lot of bearing tools - Park wheel building stand with all the bells and whistles (which i never use) Built my own bike service stand - Air compressor (Makes tire maintenance a pleasure) air gun and digital tire inflators. I even have the L/R thread taps and inserts for crank repairs.
So over time you learn basic service skills and eventually you will be stripping and rebuilding the entire bike saving you lots of money at the LBS
The best part is if something isnt done right you only have to argue with yourself and not some A/hole wannabe bike mechanic