Neck-thru! NICE!!!Here you go, Fix!:
Epiphone Thunderbird Pro-V Bass
As you can see, the fretboard is a friggin' aircraft carrier! But the good thing is (if you want to go that way), that other than the neck width and the 5-string bridge the rest is pretty much identical to a Pro-IV - Pickups and electronics are the same and the headstock is the same size with the 5th tuner added on the treble size.
So, with a new 4 string nut and bridge and removed 5th tuner, you're basically where you want to be on a budget.
However, you may want to swap out the anaemic active pickups and electronics for a passive set of chrome Chinabuckers with matching pickup rings and while you're add it, you might just get that 4-string bridge in chrome and a set of affordable chrome tuners - EBay is your frind for this...
Although the Pro-V is out of production, they do shows up now and them at reasonable prices.
Have you ever seen a 4 string conversion done like that before?