Here are a few things that I have found that completely wears my guy out and will send him snoozing in no time.
Laser play - we have a little laser on a key chain that Opie loves. He will chase that little red dot until he can chase no more. We have the most fun just watching him go after the laser and it doesn't matter if it is up the wall, ceiling, under furniture - he is going to try his best to get to it.
You can find these in the cat aisle at Petco and Petsmart and I am sure just about any store like Walmart or Target carries them. Cheap and fun!
Remote Control Toy - we bought a remote control toy at the Dollar General for $10! What a bargain! Opie just goes nuts. Of course a little barking comes with the play so if you don't mind that - it is a great tool to wear their little bodies out on an indoor kind of day. You can get all kinds. Robots, cars, trucks, etc. The one we bought turns flips and adjusts itself if it runs into furniture, so that helps.
Treadmill - now this is the biggy. We lucked out and bought a really nice used one for $100. If you don't have one - you can scan Craigslist - they are on there all the time. We have yet to master this one, tho. It is still in the works. We will get there, tho.
So - there you have 3 ideas to keep your dog busy enough to spend a little energy when a walk or the park is not an option. It won't cost you but a few dollars and it takes very little energy on your part. I mean - sitting in the recliner while he does all the work chasing these toys around - come on. Can't get much easier than that!