You don't have to go through ebay for the Spectra thread. Spider Wire (a brand name, there are others) fishing line can be found in any fishing department. 30lb test is same size as dental floss (and works as dental floss too).

I cut a piece of orange Kydex plastic, about 1" x 1 1/2" into the shape of a 2 diminsional thread spool (that's probably confusing, should post pictures) and wrapped 65 feet of line around it. I used it to replace the roll of nylon thread in the Ritter PSP. It's so flat it takes up less room than the nylon roll and there's 15 feet more of it. A real win-win situation, and it's got a million uses.