Small tooth to be built up?

I am getting my braces off in four weeks,but i have two undersized teeth at the front so my dentist suggested I get them built up by either a crown,veneer or white filling material..I am going to get it done at a cosmetic dentist surgery,not on the NHS (because there is a better colour range). I was just wondering which would be better to build up the two teeth and what is the rough cost? Thanks