You could easily change necks to a fretless. All it needs is a good setup with the fretless neck. How much is not a fortune to you. Cheaper good quality basses are the usual names, Ibanez, Cort, ESP LTD, etc.
If you know how to setup your own basses you could simply buy a fretless neck to fit and change the setup to your taste. Maybe change strings as well as rounds can dig into some finger boards with softer woods.