Do you have any old glass still? If you do and it's good, you might want to adjust your ideas.
In a couple of months the D90 replacement (rumoured as the D7000) will come out and D90 owners (even D300 owners) will be shedding their old bodies for the upgrade. It's sounding like it's going to be a truly epic upgrade... But it's way out of your budget.
But for somebody getting back in the game, a nice second hand D90 sounds like a great plan. I say this over a D3000/D5000 because the D90 has screw-drive AF whereas the newer D3000/3100/5000 do not, making them pretty useless with old (cheap) lenses.
Even if you don't have old glass, you might want to hang on, snap up a second hand D90 for a good price and then use the saved money for something like a Nikon 18-200mm f3.5-5.6 lens. Aperture is slower than I'd like but it's roughly a third of the price of a Nikon something-200mm f2.8.
I'd also say that the Nikon lens is worth the extra dosh (it's probably twice as much as the Tamron equiv) as it's sharper across the whole image at several zoom points and the bokeh is a billion time nicer. I've seen too many Tamron shots with ferociously "busy" bokeh that just detract from the whole image.
I think the extra spending in your glass is worth it as it'll a) last for a good 8-10 years and b) holds its value very well if you look after it. Just make sure you get a decent cover for it.