How can I get my husband to participate in physical activity and exercise?

Low cost equipment is available through catalogs/internet. My mom has a small frame that sits on the floor with bike pedals on it which you use sitting in a chair. $30.00. Also works on a tabletop for your arms.
Many other exercises that don't require any equipment. Check out social services...may point you in the right direction.
Bribe him with a treat.....after you do this for ? minutes we will have some fruit/yogurt....whatever you know he likes.