Welcome! Sounds like your going to building the same type of machine I built. I build one mostly for the fun of it but instead lead to carving signs and artwork. As for software, most people go for mach 3 because its easy to work with and not too bad for price. I like it alot. The price can vary greatly and depends on the materials you use to build the machine. In my case, I had no money to build the machine, but in the end ended up with a pretty solid machine. I just looked around for used parts, and materials and actually ended up using an old military bullet inspecting machine for the majority of my parts including both my y and z axis, and the table top. Take a look at
www.homegrowncnc.com, theres alot of information pertaining directly to diy cnc machines. Good luck