For me, my exercise of choice was and is walking. Not only is it cheap, but it also gets me outside when the weather is nice. Right now, its freezing outside, so a trip to the mall is how I get my daily walk in, making a big loop inside, where it's nice and warm.
On the retreat I led last weekend, I talked about walking, and encouraged those who were with me to get up and get moving. In order to help us all with developing a new walking routine, I came across two resources. The first in an article which spells out, in seven easy steps (pardon the pun), how walking can really help with someone wanting to lose weight. Click here to read the article.
The second resource is a 16 week walking journal written by Leslie Sansone. Leslie has a slew of walking/exercise DVDs that just might help get you into a new fitness program, right in your living room. I bought my used (but not written in) copy of the journal from Amazon for under $5, and that included shipping. Unfortunately, it arrived the day after my retreat ended, so I wasn't able to show it to the group. The only negative is that there's no reference to God in it, so, you'll have to add that prayer piece yourself. Remember, as St. Ignatius says, in everything we do, we need to do it, not just for ourselves, but for God's greater glory.