You need lots of things not just a marker.
A mask should be number 1 in my opinion,budget £50-£100 new maybe a little more,try before you buy.
As for a decent marker,secondhand you could pick a very decent marker for £200+ depending on what you want.
I've just got myself a gtek and love it ,I upgraded from an Etha (also a great marker )
One thing you need to Consider is noise when shooting !.
Do you like to be heard or not ?
Poppets like the etek are loud .
Spools like the gtek are quiet .
I like single head shots so the Etha and gtek fits me well .