Thumb Score: +27

Amazon [amazon.com] has Stansport Propane Converter, Converts liquid gas style stoves to propane for $5.12. Shipping is free w/ Prime or on $35+

YMMV: Possible extra $0.52 coupon on select accounts on the product page = $4.60

Walmart [walmart.com] has Stansport Propane Converter (185) for $4.36. Shipping is free w/ Walmart+ (free 30-day trial [walmart.com]) or on orders of $35+.