This ^
And de-fretting an existing neck is pretty much irreversible. Do this and find that you don't like it and you're stuffed ... you no longer have the bass you liked so much, you can't convert it back again, and you've destroyed the resale value.
+1 for buying an after-market fretless neck, then source the hardware you need (tuners, string-tree, etc.) pre-owned either here on Basschat or through eBay. No real need to buy new if you're strapped for cash.
As a matter of personal taste I've never really 'got' lined fretlesses. They don't look fretless unless you get up close and you know what you're looking for, so you get no Wow! factor, and the only person who can't see the lines is you, the player. It all seems a bit silly.
I've always preferred to have fret-end markers inserted instead. You look down at the edge of the fretboard/fingerboard and you see where the frets would be if there were any frets. I find that system to be well inside my comfort zone.