The sigma 10-20mm might be of interest - a sharp and good lens its well used by many with crop sensor cameras - if your's is not crop sensor though it won't work.
[ame]http://www.amazon.com/Sigma-10-20mm-4-5-6-Digital-Cameras/dp/B0007U00XK/ref=sr_1_2?ie=UTF8&s=electronics&qid=1225568684&sr=8-2[/ame]
amazon lists it as above your price range a bit - and it does go wider than you need, but worth a look
Shoot, if all you need is f/3.5 at 18mm, you can get the Nikon 18-55 DX for $100, although, you probably won't be happy with the build quality having been accustomed to the pro-rated lens you currently use.
Check out the Tamron 17-50mm F2.8. It should be around USD350 (or at least was when I got it), and it's a really great lens for the money. If it was weather and moisture sealed it would be perfect, but you do get what you pay for. The lens also got quite good online reviews (photozone.de, fredmiranda etc.). If you need to see some test images, you can check photozone.de's reviews, or my phototracker - every photo in my photo tracker with a focal lenght in between 17-50mm was taken with the Tamron.
If you are start looking for something even wider later on, I'd recommend the Tokina 11-16mm F2.8 over the Sigma 10-20mm F4-5.6, although both of them are not in the USD350 range.
I second the Sigma 10-20mm, but it is beyond your budget and would leave a serious gap in focal length. It is a bit slow, but as epp_b mentioned, the 18-55mm is pretty sharp but the build quality might be lacking. However, if you're gentle with your gear, that shouldn't be of a concern. Mine is still in pristine condition. I think Nikon now pairs bodies with the 18-135mm lens. Check photozone.de / dpreview / fred miranda / thom hogan for reviews.