The poor warranty and horror stories with NordicTrack turned me off from their treadmills. It also seems like some force you into the iFit platform, which just adds to the cost or takes away from functionality.
At that price point, I think a Horizon or a Sole would be good options. I believe there’s a review from Dan with a discount code (valid until 1/31) for the top of the line Horizon (7.8 AT, iirc), and that should be under budget even if you pay for assembly. Sole is an even cheaper than that and has lots of fans, the only drawback I’ve seen there is that it’s relatively slow to change speeds, which sounds like it won’t be a problem for your needs. And lead time will be an issue for both, given the market these days.