Free Home Gym Cans of food or jugs of laundry detergent as hand weightsFloor space to do pushups, squats, lunges, dips, mountain climbers, burpees, etc.( check out this no equipment needed workout )
Fitness DVDs from your public library, youtube videos, or Body Rock TV
$100 Home Gym Dumbbells - 5lb set for $6.40 and 10lb set for $20.80 Jump rope - $7.11 Exercise ball - $16.54 Chin up bar - $24.90 Yoga mat - $20.85 DVDs (my favorite: Jillian Michaels No More Trouble Zones) - $8.70
$500+ Home Gym Treadmill, stationary bike, or other cardio machine - $250-$500 (used from craigslist or garage sale) Barbell set - $69.99 TV - steal the extra one from your in-laws :)
I think searching for used equipment is always a great idea. If you ask around, you may find someone who would be grateful for you to just take it out of their garage.
Does anyone have other tips for setting up a home gym?