Yes, needles are expensive. (so is everything!)
but a size 8 needle is a work horse.. it's the MOST common size recommended for worsted weigh yarn. and worsted is such a common yarn!
I have dozens! straights, (long and short), circ's, and DPN's.
I use them all the time.. (for hats, for scarves, for sweaters, for thousands of things.)
BUY YOUR SELF SOME NEEDLES.
a size 8 circ (a long ish one) --say 36 inches or 40 inches can be use for knitting straight, for sweaters, for magic loop (for short things like hats)
You'll be happier in the end.
if you are using a size 6 (2 sizes smaller!) you are going to change not only the gauge, but the fabric of the knitting..
and while this (ABSOLUTELY!) can be a good thing (i just knit a poor boy type vest (all ribs, all the time) on a size 6, (with worsted weight yarn) --i knit the matching/coordinating sweaters (one for him, one for her, grandchildren) with size 8's..(and got a nice smooth fabric, not too thick, but certainly not 'drapey')
You can increase from now to next year, but you are not going to get the same hat (and might, be disapointed with the results) if you use the smaller needle.