I've been experimenting with Sous-Vide recipes and needed a way to vacuum-pack meats for submersion into the temperature-controlled bath. I refuse to pay $1+/bag for regular vacuum packing bags only to toss them a few hours later, so I devised a cheaper middle-ground that seems to work well.
Take a cheap hand-held brake-system vacuum pump like the in the picture below ($20 at Harbor Freight) and route the hose through a gallon freezer bag so it's sealed good enough to hold a temporary vacuum (for a few seconds anyway). You can see where the hose pierces the bag on the bottom-left.
Take your food item and place it into a quart-sized zip-lock bag, preferably one of higher quality like the twin-zipper kind for a better seal (~$0.10 ea). This bag must hold the vacuum for the duration of the cooking cycle. Being under water extends the life of the vacuum, so if it lasts 3 hours sitting on your counter, it might last 6-12 in the water bath.
Leave the quart baggie partially open so air can be evacuated from it. Place this with the food inside into the gallon bag and seal up the gallon bag.
Begin pumping the air out of the gallon bag, which also evacuates the quart bag. When you have achieved a good enough vacuum, just press down on the quart bag's seal from outside the gallon bag and then open the gallon bag. Now you have your food vacuum-packed in a quart bag. For a while anyway, depending on the quality of your bags.
I've used this method with steaks that went 5 hours in the bath and they were still well sealed afterward, so that's good enough for me. You can continue to use the same gallon bag unless it becomes contaminated.
A couple other vacuum-packed items using this method:
If you're looking for a cheap bath, mine consists of a $10 crock pot with a $10 electric water heater thermostat screwed to the basin. It has a range of 95F-150F which is perfect for beef. When set at 133F it fluctuates from 131F to 135F (med-rare).