Is there any particular reason you are set on running SLI? A recent article here on Tom's discussed how setups with lower end cards in an SLI/Crossfire configuration suffered from micro-stutter.
Your best bet might be to take your full budget and sink it into one card. $300 should be enough for a GTX 570 or a HD 6950. Both of which are great cards. Plus, it'll leave you the option to go SLI/Crossfire later.
I was thinking of running 2 EVGA GeForce GTX 550 Ti Superclocked 1024MB in SLI. Thay are priced at $130 a piece.
I'm just looking for suggestions for alternatives in this price range, and I would like to use Nvidia Cards in SLI.
As an alternative, spend $260 on a single good card. If this is a new rig, you will also spend less by not needing a sli capable motherboard, or a stronger psu.
The main reason is that sli of low end cards is more prone to microstuttering. Even though benchmark FPS numbers may be higher, the annoyance factor is also higher.
Read more here: http://www.tomshardware.com/reviews/radeon-geforce-stut...