I am doing a very similar thing. I love... I mean LOVe my Ibanez GSR 205 I got back in 2000 or 2001... or 2002? Anyway I love it so much I've fallen down stairs with it etc so it is pretty beat it. I do try to take care of it though.
Anway recently I found one on ebay for 150 and I love how the bass feels... the neck. The body weight seems perfect. I pick up 1000 dollar basses and I think meh... my gsr could take it.
Anyway, I got a mirror twin. I scored a beautiful Hipshot Gold 5 string A-style bridge of ebay($34 booya!). I bought some replacement tuners wilkinson open gear gold (please tell me if these are garbage). And some other random gold hardware, knobs etc. I've used a heat gun on it to remove some paint and plan on removing all the paint soon. I expect the wood to look like vomit underneath and at the point I'll use some kind of solid green paint or something. If the wood looks nice I'll probably stain or oil or something to give it that woody look. I've even scalloped the frets from the 12th down to the 20th or whatever it has(don't worry about telling me if this was a mistake or not I'd like to find out on my own).

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So to make a long story short. If you like how the bass feels, weighs etc then you can always change how it looks, sounds etc. I'm having more fun doing all this to the bass than playing it. I think for most people though it is better/cheaper to just save up and buy a nice instrument. Electronics seem to be very tough to gauge though... you really need to know what you want because a 100-200 bucks down the drain really sucks. At least buying hardware its easier not to mess up.