£100 is good but check Ebay and phone around a few dealers, we got lucky when we found a local Citroen dealer flogging a set of four new steel wheels for a C1 for a few quid each. If you buy from a scrappie be sure to get them to agree that if any wheel turns out to be wobbly, they will refund your money as some will have come off crashed cars. Count on a tenner each for tyre fitting and balancing and warn the fitter to spin the wheels before they start in case any are wobbly.
Winter tyres are ace; you can go out and play in the new snow when everybody else is cowering indoors worrying about bread and milk supplies.