Not much wrong with the Rincon frame. Your wheels though will have a screw on freewheel rather than the more modern cassette and freehub. So an upgrade to 9spd or 10spd will require new wheels and groupset. This'd require an investment over $400...assuming a Deore group and wheels but it would bring the bike up to modern equivalent spec of a $1,200 plus retail bike. Here's the groupset I'd be looking at
http://www.merlincycles.co.uk/Bike+Shop ... OUPSET.htm As for wheels...the Star wheels from CyclingDeal can cope with rim brakes for $100
http://cyclingdeal.rtrk.com.au/?scid=31771&kw=3914562 If just the crankset is knackered I'd consider just replacing that either with an Shimano Alivio (which uses a tapered BB - that you likely already have) or a Deore (uses a Hollowtech BB). Advantage of the latter is replaceable chainwheels and light weight. They also come with the BB and can be had for around $90 online.
http://www.merlincycles.co.uk/Bike+Shop ... t_1939.htm Given that a new BB would be advisable anyway (and perhaps a new chain - suggest KMC X8.93) it could be a good option.