You don't mention if you're dealing with any motor delays, but if you are, look at the category OT on pinterest. Otherwise, things that have worked well for me after 12 months (at encouraging gross motor play/movement) that didn't cost hardly anything:
Climbing: small cardboard boxes stuff with newspaper to climb on, couch cushions
Crawling: large ridiculous pillows/stuffed animals/couch cushions (from the thrifstore/yardsales/free on the side of the road)
Novel terrain: parks, playgrounds, municipal buildings where there's lots of steps and things with different heights to negotiate. Good workout.
Push toys/Rolling toys: Encourages a lot of skills related to prewalking/walking
Swings/hammocks/etc (see DIY swings, therapy swings, etc instructions on the internet )
Exercise balls, big balls