The best professional-grade sax for the price will be a used sax with no structural damage, that is still in good enough mechanical condition where it might only need a few pads replaced and some regulation adjusted (for $100 or so). With the economy still sluggish, this is still a good time IMO to pick up a used sax. Any of the "big-four" established brands (Selmer/Yamaha/Yanigisawa/Keilwerth) is do-able at $2.5k, especially for an alto.
$2.5k could also get you a brand-new Cannonball or other quality Taiwan-made brand, with hundreds to spare on a really nice mouthpiece or two. You'd take a real hit, though, if you wanted to re-sell it. Accordingly, for $2.5k, you could get a used Cannonball/Barone/TKmelody/MACSAX tenor AND a used alto in decent shape.
Whatever you decide, TRY before you buy if at all possible!! Find a sax that feels comfortable under your fingers, and has a tone that sounds pleasing to your ear. As Mr. Thomas notes, sound quality from individual instruments of the same make and model can vary greatly (and disturbingly).
Good luck to you!