Well, here is a place you could check buy a lot of tea in bulk on sale this month. If you are looking for something really strong, then probably fukamushi sencha or konacha will do it for you:
http://sugimotousa.blogspot.com/
(This just gives more details on the sale, and links you to their actual company website/online store)
Another idea you could try is powdered sencha:
http://www.denstea.com/index.php?main_p ... &cPath=268
It will be much cheaper than matcha (may have more bitterness, but it sounds like you don't mind that), will have a lot more caffeine than if you just steep the leaves, and isn't a terrible price. Here is one place you can find it:
http://www.denstea.com/index.php?main_p ... &cPath=268