At under $500 for a 25/28 there are somewhat limited choices. The P lenses from CV, the 21/25 are extremely good for the price. The best fit in the range you are looking at would be a 28f3.5 Color Skopar, though you have to factor in a screw-M adapter here. Also the now discontinued 28f1.9 Ultron would work well - again, factor in the screw-to-M adapter in the price. The 21/25's does require sep. viewfinders which add $135-150.
I dont know what Stephens price will be on the new 28f2.0 Ultron, but as for performance, it is staggeringly good!I have posted 80+ shots with it on our Flickr site and the more I use it, the more impressed I am.
Used lenses might be a better choice and there is a bewildering array of those, Snap Shot Skopar 25f4, Canon 28f3.5 and of course, there will be a fair amount of used VC and potentially ZM Biogon 28f2.8's once the Ultron 28f2.0 is out and available.
I would keep an eye on the Classified's and see what pops up. RFf members tend to have a more realistic view on value than E-bay anyway.