If you have access to a workshop you could build a small scale motor-generator rig using a truck alternator. Commercial vehicles use 24v so I would imagine that the alternator output would be near 28v. As you're on a budget, you could probably find something suitable at your local scrappy. And an old washing machine motor will do the trick just fine. Remove the rectifier pack and run the the drive motor via a speed controller with a tuned circuit feedback loop from the AC output. You will just need to know how many pole pairs the alternator has to determine the motor speed.
Much more fun than just buying something off the shelf!