do you have a car? Set it up on a flat stretch (or slight incline so it doesn't get away from you) and push it along.
Seemed to work for Conan.
(I'm just some beginner, don't look to me for any reliable advice on nutrition or working out, other than what I've been told by others, or what seems obvious)
I'm body-weighting this week as I'm away from my gym,
Push ups (feet raised on a chair, regular, diamond, etc etc)
Pull ups (off edge of balcony, but you've got a bar, so use that, duh)
Inverted Rows (if your bar is one of the fit-in-a-doorway ones, you could just lower it)
Squats (use your DB like BigNurse said)
Dips (Chair again)
I like to do situps or plank for abs, but rollouts are probably more manly.
For me the biggest problem of not having a gym is not that I can't find a way to do some exercises (I like to over-head press my kayak) but the discipline of starting (and finishing a workout)
you might be a better man than me, but if not: treat it like a trip to the gym, set a time, remove all distractions, get some music or whatever floats your boat (Flex Arm Hang for a play through of "Shine on you Crazy Diamond" ) and plan the routine.
Pasta, Potatoes, Rice & Bread are all cheap. (I tend to avoid Bread and Pasta, not for any scientific reason, they just remind me of fat people)
Mince (or Ground Beef, depending on where you come from) is cheap, and with a small investment in 'erbs and spices, can be made to taste less like Rectum.
I like to tackle plenty of fresh fruit and veg, the kind that can be eaten raw, and broadly speaking (as long as you avoid truffles and bananas*) is cheaper than your average bag of crisps and a coke.
To make rice less goddamn boring, I cook it with various beans, and more 'erbs and spices.
Eggs are pretty cheap, and you can make more or less anything into an omelette.
I also like to drink Beef Stock, I have no idea if it has any beneficial qualities whatsoever, but it makes me feel manly, and psychology is half the battle.
Someone will mention food logs and the like, the general concensus is "keep one"
*Banana Famine in australia, very serious, don't want to talk about it.