1. I would try to work out in the morning. After 15 hours it would be very hard to get motivated. But you aren't me, so who knows.
2.Walking/Speedwalking/Running would be relatively inexpensive (but you need good shoes).
3.You can do great things with body weight exercise. If you started out doing pushups that works a lot of upper body at the same time:
Check it at an angle (which is easier than the floor, move down in angle as you need to make it harder stairs are fabulous):http://www.youtube.com/watch?v=PouVQ65LjOs
Squats are also really basic and functional:http://www.youtube.com/watch?v=qRnGI3c5Jjs&feature=related
I suspect you are too heavy to do pull ups (who isn't), but you might manage some table rows? Not for rickety tables.http://www.youtube.com/watch?v=9E_1onVeY7k
I would start out aiming to do one set of 8 repetitions of whatever, then add one more repetition the next session if you can and so on until you get to 12. Then in sessions after that see if you can do a set of 8, rest, do another 8. When you work up to 3 sets of 12, make it more challenging.
4. Sandbags can be used for weight on the cheap. After you do this body weight stuff 2 to 3 times a week for a couple of months make one yourself a sandbag and take things up a notch:http://www.youtube.com/watch?v=vpo7XyIlV_Q
Then what to do with ithttp://www.youtube.com/watch?v=Y3-uagl55-A&feature=related
I strongly suggest you Google instructions on proper form on the exercises named so you know how to protect you lower back. If you took my advice about lots of pushups, it will already be a bit stronger, but still. Keep the weight light to start, and take things slow. You can add more gravel later as you get the hang of it.
And that's about as inexpensive as I can suggest. You might check your library for "body weight exercises" or basic weight training books to educate yourself more than listening to a random yahoo on the web. I personally love The New Rules of Lifting for Women, but it's kind of heavy on the fun equipment like balls and cables or bands and such. Exercise bands are also a pretty cheap alternative, but this post is already too long. Oh what the heck:http://www.youtube.com/watch?v=QJBOFbB1RGE