There's gotta be a cheaper way to get kite lines. Is there anything that's as strong and fit for the purpose that I can buy from a hardware store? I think Kite Lines should cost $30 to replace. Not $150
The initial cost for lines is going to be similar, so go with the lines that last longer. That is where you will realize a savings.
Q-power are still a bit less expensive because you can get 6 lines out of a $140 spool of Q-Power. This means for $280 (2 spools) you can get 3 sets of lines(four line kite) that last at least twice (guesstimate based on my experience) as long as the lines you get from Kite companies. Because Q-power lines last twice as long, you are effectively paying ~$47 ($280/3 sets = $94 then $94/2) for the same amount of use you get out of a $150 set of lines you buy from a kite company.
Saving $103 per a set of lines is significant in my opinion.