Well, I'd obviously immediately push you down the road of either Fender Standard Jazz/P bass, but there is also the Squier Vintage Modified Jazz/P basses which are supposedly hot shit. You can't really go wrong with a Jazz bass.
But, from first hand experience Aria have nice basses. Nice thin necks that makes an easier transition from guitar to bass, in my opinion. The IGB-35 stands in around $400.
In the same vein theres the Yamaha BB424, which are very nice, well built basses. Again, they're hitting about $400, but they sound fantastic.
My very limited knowledge of bass knowledge for you there! You could always go to Rondo and pick up a Violin Bass for hardly anything and be the envy of any McCartney fans you have as friends/bandmates.