Yeah, but hang on - a bloke wears a wedding ring too.
Blokes wearing wedding rings? Bit too American for me. Don't do jewelry.
Re the OPs question my advice is ask the girl what she wants. Getting one she doesn't like but feels obligated to wear is bad. Buying too cheap makes you seem a tight-arse yet spending too much when you'll doubtless want to buy a house together and so forth would seem stupidly extravegant.
There's a whole industry dedicated to selling stuff to engaged couples. Whe had a fairly big wedding, yet kept the cost within bounds by not getting carried away with friperies. Great venue, yes, great food (buffet), yes, lots of guests, but not much else and no photographer - as that tends to dominate the proceedings and turn an important emotional celebration into a glorified photo shoot - and saves a good bit of dosh. Another good hint is to marry in February - you can get a good discount by a bit of haggling ! Honeymoon on Skye was also not sold out for some reason.
My wife doesn't really bother with jewellry so she didn't want an engagement ring nor even a wedding ring and as a down to earth northern lass determined it was a waste of money. Somewhat to my suprise she did change her name, and I'd not suggested she should or shouldn't.
anyhow, my advice is ask, unless you're very sure of what she'd like