Ok...
Firstly, are you really surprised that a tyre shop - who make their money selling tyres - will charge you a lot for fitting tyres you've not bought from them? Really? Didn't think so.
You can find places that will swap them for you cheaper. Typically it will be a backstreet race-bike mechanic somewhere rather than a big bike shop - they're geared up to swapping part-worns back and forth for racers. I've got one locally that will do them for �6 a wheel, but that's not much use to you.
However it's worth doing your own occasionally to keep your hand in in case you need to do it on the trail. And TBH I've been swapping mine so often lately that even �6 starts to look a bit steep
Rear wheel nut is 22mm. Front spindle is a 14mm hex key. Neither is included in the toolkit (cheers Yamaha). Go to Halfords/etc and look for sockets to fit car gearbox drain plugs.
I wouldn't bother with rim locks for normal trail riding. I don't think it's particularly sensible to run very low pressures on such a heavy bike anyway. I run at about 25psi, and that's enough to stop the tyre spinning on the rim.