If you can afford time search ebay for bmw wheels/tires, etc but select "items in my region" afterwards. Often the biggest cost is shipping depending on where you are you can save $$ right there. Being in SoCal you should find lots of rims for sale. All e36 cars (such as your 318ti) have the same lug spacing (120mm) and offset (46mm I think, anyone?
). It's only when you stray from that you need spacers etc. Don't go too wide or you will rub in front. Search this forum for actual sizes, comments, etc.
Be aware that upping your rim size should not affect your ride height as the tires get thinner as the rims get fatter. What does hapen though is your "wheel gap" becomes accentuated when the tire profile (sidewall height) reduces. Running 17's on a base suspension ti will look like your 4-wheelin it through the mud bogs. Not pretty. Get a nice set of 16's and your ride will be nicer, tires cheaper and it still looks OK with the base suspension IMO. And like J!m said, tirerack is a great place to start.