Correct me if I'm wrong but the SA stuff is not fluoro. High quality fluoro like Seaguar Gran Max and comparable Rio products is typically $12-20/25 yd spool. InvisX is likely the same product and is extremely cost effective. The Seaguar normal Fluoro (not fly fishing specific and not double structure) is also a really good deal at most gear shops.

This is the SA fluoro and it's all above $10/spool: Scientific Anglers Fluorocarbon Tippet with Cutter 30-meters by Scientific Anglers http://www.amazon.com/dp/B009M9XVGU/ref=cm_sw_r_udp_awd_h-igtb0WP1JVC