Cheapest I've found for non-lab use is Nasco Farm & Ranch.
No, I'm not kidding. :)
You can get it pre-mixed (http://www.enasco.com/ProductDetail.do?sku=C15197N), or dry (http://www.enasco.com/ProductDetail.do?sku=C08175N). I prefer dry because you can mix as much as you need, and no more - the cellulose base *does* go bad after a while. Also, you can add the dry powder directly to white vinegar, and make a kick-ass soap scum remover goo.
Re: Where does one buy PEG?
No, I'm not kidding. :)
You can get it pre-mixed (http://www.enasco.com/ProductDetail.do?sku=C15197N), or dry (http://www.enasco.com/ProductDetail.do?sku=C08175N). I prefer dry because you can mix as much as you need, and no more - the cellulose base *does* go bad after a while. Also, you can add the dry powder directly to white vinegar, and make a kick-ass soap scum remover goo.