|Don't know if this one is already in the tip list or not -- but here goes.
I used to buy serger thread four cones at a time (for my 4 thread sergers). However, ever notice that you use much, much more upper and lower looper thread than you do needle thread?
So, try using only two cones instead of four! Just thread two bobbins from a serger cone -- and use the bobbins for the two needles. Bottom line, you have two bobbins feeding your two needles and two cones feeding the two loopers. Instead of buying sets of four same-color cones, you can get by with two same color cones -- and just buy many more colors!