Following up on Vanhalo's Costco DIY suggestion, take a look at this video for a cheap and simple solution. Basically, shock cord, 2 hair ties, and 4 pennies. I added double barrel cord locks to make it a bit more adjustable. Just slide the cord lock onto the shock cord before you tie the loops on the ends. Worked out fine, other than the fiddle factor. Took it down to the mid 50s. Not sure how far one could push it, but I think I was close to the limit.