Sorry I would suggest custom. there are some websites that are a bit cheaper. Did you try Smith + Noble?

Smith and Noble is not exactly what I would call cheap...if you do need custom, Etsy may be a good place to look.

I'm having a similar sort of problem finding drapes I like. I found the perfect thing but they're cotton shower curtains, and therefore have holes in the top for hooks AND they're too short. I bought extras (they were only $20/ each and 72" wide). I'm going to take them to someone who makes custom drapes, and see about having them pieced together to the right length with a rod pocket on top. At the seam where they're put together, I think I'll ask for piping to make it look intentional.

Could you find ready-made drapes that you like at a good price, buy extras, and have someone make them longer for you in a similar way?

I've had great luck with pottery barn 120" drapes, when they are on sale. Still not what I would call cheap but...affordable and they last forever, even with 3 kids and 6 dogs. I have also purchased multiples of a shorter drape and pieced them together to get the right length and used a wide braid, or trim at the seam.

in one of the houzz idea books, there was a link for a budget makeover and they used drop cloths. Let me see if I can find the link as I just looked at it today.

here;s the link the post this is in was actually posted in design dilemma and is titled Great Room Makeover Help

http://www.lindaholtinteriors.com/2012/10/more-budget-saving-tips-from-necn-room-makeover/

Have you considered just hanging "panels" to divide the windows on 12 - 18 inch rods. If you don't need privacy, you might want to consider this. You'll have a lot more options in fabric styles and weights. It would certainly be a diy project if you skip the pinch pleats. I am just dying to do it to my front picture window. I love shoping at Overstock.com. It's super fast shipping and they have a very large selection. Here's a link to a picture... not exact, but you'll get the idea. http://pinterest.com/pin/94786767128363295/

There are plenty of sources... Try googling 120" drapes. I am looking for the same.

I do them all the time. Wonder what you mean by cheap (budjet) The trick is to get someone who knows how to find cheap but good fabric, then has a workroom to make exact size you need. There are some of us designers who can get just what you want and need without charging too much. It's easy! Painless, and fun!

depending on the style of fabric you want, you could also look on ebay. people sell drapes that they no longer want/need, and i'm sure you could find 120" long drapes there.

you just have to be willing to sort through the listings.