Zoesandra, a dwf member, used to offer this service on ebay for ~$100. Dont know what depth of plate it was though, I suspect it would be very thin?
You could also do a quick google for something like 'gold plating solution'. I did one and got loads of links like this. Mind you some, like this link use cyanide, so be very carefull when you use it, but others are much safer.