Our banner last year was done by FedEx Kinkos, in about a day for around a hundred bucks. You can see it on the right in
this picture, but it is a bit taller (he folded it up so we could see his head, at the top it says "Jupiter High School & GE Healthcare", so roughly two feet taller) and vibrant in person.
This year however, we are working with our t-shirt supplier to use vinyl on a laarrge banner. Talk with your shirt company once you have chosen one and see if they have a reasonable deal. It might also make them more open to giving you discounts on your shirts such as waving the setup/screen fee (if they are feeling nice - this is the main cost of shirts. Typically between $30 and $50, per color, each side of the shirt. This is why you want to keep your logo simple for the shirts, and use as few colors as possible. This year we are ordering over 150 t-shirts, the screen fee was waved, so the cost per shirt came to ~$6.75). Always try and negotiate a cheaper price, and offer to the company their logo on the shirt.
Anyway, good luck, and get moving... the earlier, the better, don't want to pay rush fees do you
