Check Newegg or Tiger direct. I think Newegg is cheaper but you can run into deals at Tiger too. Stick with brand names check the reviews. Asus, Gigabyte and Abit are good brands. I have never tried a DFI board but the user reviews are excellent. You can also take a chance on an open product and get a more expensive board for under $100. I have seen the Asus M2N Deluxe SLI for under a hundred (open package) If you try an open package. Read carefully.
You didn't mention cpu cooler but here is a recomendation;Thermaltake CL-P0401 110mm Full-Range Fan CPU Cooler - Retail
It's expensive at 60 bucks but it does the job. I don't know how hot a 2.8 gets but my 3.2 has had heat problems. I ran a water cooler that kept it down to 45 degree range (In AH) Pulled the whole system out. Dropped the SLI 8800GTXs, put in a 8800GTS. Removed the water cooling. Added the Thermaltake CPU cooler put it all in a Antec nine hundred case. Now I run 35-45 degrees. Usually under 40 degrees after 3 or 4 hours of AH. (I also had issues of too much stuff, too little PSU, dropping SLI fixed that)