Its not a case of the cost, its more a case of trying to find one. They are just so rare. It is possible to find a genuine 70's one but then we are talking silly money into £2k - £3k territory which I don't have, or want to spend on a bass that will be a regular working bass. I've also not seen a Mexican unlined fretless bass ever, only American and Japanese and again they are so rare. I don't understand why Fender don't make a standard unlined fretless Precision and Jazz for those that want to play fretless. Apart from Jaco, I don't know of any named bassist that plays a lined fretless. Pino Paladino, Sting, Jeff Ament, Derek Forbes, Tony Levin, Tony Franklin, Mick Khan, Percy Jones, Bakithi Kumalo, Jack Bruce, John Giblin plus many more all play unlined. I'm sure there are known players who play lined but the majority are unlined.
I'm not worried about the value from resale as its not something I will ever sell on.