Hi there! It's awesome that you're expanding your flip flop business and considering adding them to your craft fair lineup. When it comes to sandal lasts, I understand your budget constraints. A good alternative could be looking for local shoemakers or cobblers who might be willing to collaborate or provide you with some insights on strap measurements for different sizes. They might even have some lasts they could loan or sell at a reasonable price. Additionally, if you decide to source them online, make sure to do thorough research on the seller's reputation and reviews, especially if they're from overseas. And yes, measuring straps at a shoe store could be a helpful hands-on approach! Best of luck with your flip flop venture!