Where are you located? Anywhere near Melbourne? If so, check out Bass Centre. Just go in and play everything in your price range. Or they do online sales - their website is worth looking at anyway.
If you like the RBX270, you're going to want something meaty with a bit of bite from a neck pickup. I have the same bass. It's still awesome, btw. The Ibanez SR505 is in your range and will do the job, but there are heaps of options. I believe Bass Centre is offering Lakland Skylines in the vicinity of your price range, and Jacks Music (spelling?) in Canberra could swing a G&L Tribute L2500 for well under your budget.
Yamaha Club #247 | Eden WTDI Club #27 | Epiphone Club #153 New Rose Hotel
| ambient / electronic / downtempo