how much (roughly) would it cost to customize a fret board inlay? like i really wanna have somethin like a Jem vine or some other flower type inlay like this http://www.jameswattsguitars.com/images/short-vine-inlay.jpg
I really don't know but that should be kind of expensive
It would be expensive, and to do it you'd probably have to find a guitar customizing specialist to give you a quote on it.
it would be cheaper to buy a new neck, unless of course your's is a set or beck through guitar, then you'll have to get the fret board cutomised, i'd make a guess of over £150