I don't fully agree with linberl if you can do the work and you've said you've done upgrades before. The rear wheel is going to be annoying to find but a shop that specializes in these should be able to get you a basic rear wheel for around a hundred. From there a 9 speed chain, cassette, shifter and rear derailleur will set you back another hundred, maybe less. Alivio components are sturdy and reliable and about as nice as you need for a bike like this. You can go with sram cassette which I think are nicer than Shimano at the lower end and a kmc chain will set you back another 15.00