Go for 205/50/16 tyres - same rolling radius as 185/55/55 but cheaper and wider range. Obviously you should only fit a matched pair front or rear. For a cheap spare, better than space saver or tin of gloop, buy a 14" steel wheel (I got a brand new one for £5 of ebay) and fit a 175/70/14 tyre. Note you will need different (steel wheel) wheel nuts for the spare, as the nuts for alloy wheels have different taper.