well im far from a "tool guy" but i have used a few circular saws before.
the one i bought not to long ago was actually a Chicago tool from HF, iirc i paid 35.99 for it.
obviously if you're looking at dewalt then money is'nt a big concern here, and dont get me wrong dewalt does make a quality tool.
none the less im very pleased with this saw it even came with a pretty nice blade.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95004but like i said if you can afford teh dewalt then you can't go wrong there just a lot more expensive.. although it might (actually probably will) also last longer.. but hey for 35 bucks i can't complain a bit.
EDIT: oh i forget about support, ya pretty much anything will work for support.. saw horses are'nt to much, you can get the wood ones that will take 2x4's good cause you can replace when you cut though them by accident.. or you can get some cheap plastic ones from HF, they work fine although not easy to repair if you cut though them.
or you can just use any other surface, basically you just need to get the section you're cutting off the ground so almost anything will do.