Personally I dont think its exactly a good idea. I think the much smarter option would be to use your roughly $21 a week and buy in bulk.Take off that 50 cents a day and you've got $17.50 a week. Although that is very low you can still work with that. I live in the UK so ill give you advice based off what I buy as a student. So you've got around £11.50 a week.

First you need to to get a few veggies in your diet.I'd suggest getting a big bag of unwashed carrots.

They can be very cheap, around 60p a kilo here, get 2kg to be safe.Although look around and see whatever is on sale but you should be able to find something for less than a $1 a kilo.

You're also going to want to get something dense in calories. I personally suggest rice.Over here I can get rice for a cheap as 40p a kilo. Get 2 kilo's of that as well.

That's now your real core stuff down, but you also could do with a good source of protein.My personal preference is eggs. I can get 1/2 dozen eggs for 50p over there. So say you have 3 scrambled eggs in the morning , every morning that 4 packs so, so another £2 so.

£7.50 left! We're doing okay so far. At this point right now Id say buy yourself a chocolate bar for £.75 just to keep yourself from suicide from boring diet.

Another great source of protein I use is Kidney beans. At £1 per 500g of dry beans you should get one of thise aswell.

Rice can get boring on its own so you should also get some chopped tinned tomatoes to make a sauce of some kind.Cook that with the carrots and kidney beans+ rice and you've got a nice meal! I can get them for £.30 a tin so get 5 of those for a week.

With the remaining £4.75 I would strongly suggest bags of frozen mixed veggies. I can get 1kg for £1 so I would get 2 of those also for the week.

Now with the remaining £2.75 buy a pack of 6 apples for £1 or so.

With the remaning £1.75 either save it up over the next few weeks, or buy yourself a nice danish pastry. Your choice.

Hope that helps and good luck!