I've owned a ridiculous number of 8-strings. Was only playing 8-strings for around 5 years at ne point, so really got into them.
A number of the cheaper import ones often have issues. If they used cheap soft maple frmthe ncks they bow. I have found a number of them have bad neck pocket angles, where you cannot lower the qction enough. Also a few also set the bridges where they do not drop down low enough. Some set the bridges in body slots and they are mounted off and hit the edge of the routes. Also, some brands do not use eight string saddles....avoid those, as you cannot intonate the octaves and will be oit of tune.
If you could handle a long-scale, I would have seconded the motion....a used Carlo Robelli is the ticket. That is actually Sam Ash's store brand. They bought the old name and revived it with imports.
But you would have to like silver sparkle...that was the only color they came in I think. It was sort of a copy of a Hamer B8S, except in a 34" scale.
Old Yamahas from 70s are decent, if you can find one cheap enough.
Aluminum neck Kramers are short scale and sometimes pop up cheap. The earlier pointy model has a 4-saddle bridge but you can swap it out easily. The rounder later body has 8-saddles. They are a little heavy but not crazy.
Old Hagstroms from the late 60s are short-scale and used to be cheap but no longer. The originals were nice, albeit very guitarlike. The reissue HB-8 above is OK but an import, sometimes with some of the issues I mentioned...like bad neck pocket, etc. plus, I think those use a 4-saddle bridge. You could swap that out with a Schaller 8 bridge for $50 bucks used.
Hamer made some of the absolute best 8- and 12-string basses but are not cheap. Their B8S model is the short-scale one. They also made a handful of medium ones of that model....technically a B8M, also called a Blades Bass (after Jack Blades of Nighranger.)
Recommendation.....
Due to lack of cheap short-scale 8-strings currently being made, you may wany to consider converting a used Fender bolt-on and slap on a paddle heqdstock neck. You can pick both up for under $100 each. All you would need after that is a decnt 8 saddle bridge like a Schaller....four octave tuners and an 8-slot nut. You may even be able to just add slots to the existing nut. So, maybe $400 total cost and a little work to make your own. I may have a used Schaller 8 bridge if you go that route.
For instance....
http://www.ebay.com/itm/Squier-Jaguar-Short-Scale-Bass-w-Broken-Truss-Rod-for-parts-or-project-/322029557094?hash=item4afa751566:g:wZkAAOSwh-1W2yothttp://www.ebay.com/itm/EDEN-30-Short-Scale-Fretless-Paddle-Bass-Neck-Maple-Rosewood-NO-Inlay-/151973774106?hash=item236257c31a:g:GUYAAOSwZd1VZmrp
