Don't buy a treadmill. Trust me, you will get bored and find it difficult to stick to your exercise routine. It's much better to go for a run outdoors in the fresh air, see some sights, and it's $2,000 cheaper.
Precor has recently come down in price to around your price range. I've had my elliptical for two years and I use it regularly, through rain, snow sleet because it's indoors.