1. Volleyballs and lots of them
2. Ball Carts (two)

With these one can do a LOT.

3. A chair to stand on
4. Cones
5. Floor tape that does not damage the court

Dawn, you need two things for sure; balls and a net. I've been organizing the program for my small private school for the last 7 years. I know what limited resources means. We beg or borrow almost everything we have.
Find tournaments and see if they have balls to sell. Sometimes they buy new volleyballs for the tournaments and then get rid of them right after. We get ours half price that way.
A ball cart is a nice convenience but if you can't beg the high schools old one when they replace it and a $100 is too much. A large plastic trash can is a workable replacement.
You can use a tie top trash bag for transporting the balls. The flex guard type work pretty well, or for a couple bucks get a large duffle bag at a surplus store
This is all the equipment our school has ever used. It's more important to be able to teach the game and proper techniques then good equipment. We've never had new equipment of any kind and nothing beyond a ball holder and old net system(old as in guy wire setup), and our teams have made the playoffs each year and into the championship game 3 out of the last 4 years. Good luck.

I have this thing that straps to your waist. And a ball is attached at the end by a string. And that helped me a lot with my overhand serve. But you have to take it easy. Because when i first did it I used it everyday after school to get used to serving overhand and to make the serve hard, i hurt my shoulder so make sure u only do it like every other day.

I'd recommend a volleyball spike trainer. These can range from simple hobby grade wall-mounted, basketball-hoop mounted, or tethered ball, to a higher end unit like AcuSpike (www.acuspike.com), which is more durable, would release the ball, and be more of a team training tool.

www.acuspike.com