It depends on the device and how tightly it is locked. You can many times get a compatible sim for a prepaid contract for almost nothing. They assume you will load time to the sim but most do not have a requirement. The key will be if the device will accept a sim from another provider. If it is a large provider they likely have prepaid plans and you could buy the very cheapest they have and many are in the $10 range.
Many times you can put sims in from canceled devices from the proper carrier.
It really is going to depend a lot on the particular device. Most just care there is a sim chip in the device the don't actually require it be activated.