ok here a couple of fast answers (no afiliation with any of the mentioned parties)
a good place to stay:
www.patiosuizo.com run by a swiss couple, located in Av. Condell 847, in Providencia, Stgo. prices seem reasonable, they are close to the metro and have parking for bikes.
mechanics: I wouldnt take my bike to any other place as BMW ... they are not cheap - but still cheaper than having a shade-tree mec. screw up your bike ... address @
www.bmw.cl (its the same address 4 bikes, tho they dont mention them on their site)
www.mapcity.cl -> great place to hammer in addresses and you get zoomable maps and direction on how to get there.
cash machines are everywhere in the "better" part of Stgo. the are called REDBANC - just make sure you have a PIN on your ATM card - and chances are great that your UK-ATM card works here!
Stgo is not that great a city, somewhat newish, stressy, w/ lots of contamination in winter ... doesnt compare to the rest of the country
another point (and this is my personal opinion only) ... its not worth the hassle to either bring over your own bike (too many variables that can go wrong - Murphy was chilean) or to buy a used bike (expensive, often poorly maintained, quite some foot-angles in the paperwork) ... so the best option should be to rent a bike. However if you feel you should buy a used one, drop some info here, I think I can talk you through.
if there are any more specific Q's - I gladly answer
cheers
al
