If you wanna go the cheap route, you can do it for as little as $600 + machine fuel. Check in your area for new development (ie. digging basements, ponds, etc.) and see if the excavating company would be interested in dumping the fill on your property. Sometimes they will do this for free because it saves them from having to go to a far away dump site. Or start calling the local excavating companies and see what they'll offer. You'll need at least 5-10 semi loads to get started, but the more the better. Especially if you want tabletops or berms. Even a longer whoop section takes a load or two. Smaller doubles require the least amount of dirt. When we build a local fair race in the grandstand area at the fairgrounds, it usually takes about 20+ semi loads of dirt, but that includes a few tabletops. We've been lucky with our personal tracks to always score free dirt, although some of it has been pretty nasty with stuff like rocks and concrete which need to be buried in an obstacle like a tabletop. And for track building, check with equipment rental places. Most will rent a Bobcat for the weekend for around $300. Sketch out a track design, get the dirt dumped roughly where you want the jumps, whoops, berms, and have someone skilled with running a Bobcat and building tracks to put it together in two weekends (they have lights - you can work day and night). Of course a small dozer (good for berms or scraping) and a small loader (good for moving dirt/tabletops) would be nice too, but you can do everything for an AX sized track with a Bobcat. A rubber track Bobcat works best (tracks are nice for packing in and can also be used for forming berms), but most rental places will only have wheeled ones available.
Good luck and have fun! :cool: