buy plastic culvert pipe:
yes, it's corrugated, but you can still slide it really well, and it's fun because it vibrates your feet. Also set them up on the top of quarter pipes.
also, go through a junkyard for pre-made rails. Using old lift towers is fun. Buy heavyweight plastic barrels for jibs and bonks, put them sideways, straight up and down, whatever/
build your own boxes or rails. I always though that making rails and boxes identical, and setting them up identical would be cool, because you could learn a trick on a box and then try it on a rail that's set up exactly the same. Flat down and Down flat down are good, obviously make some flat rails and flat boxes.
as for snow features, if you made a jump that jumped up over a roller, it would be realllly fun. you could hand drag, butter, tap, whatever. here's the idea:
obviously step ups to snow butter pads are always fun as well.
Basically, you don't have a lot of money, so be creative. Buy junk! use it!
also, you neeeeeed to remind them that if they want a successful park, make it legit and safe the first year. If they try to half ass it the first year as a test run, then it won't be recieved well.