Can anyone recommend any good but cheap security cameras that would be able to film homemade porn?
Look on eBay there are many different types. Are you looking for a spy cam? If so,please bear in mind that it is illegal to film someone intimately without their consent.
Here is some info about less expensive options to concider .
https://www.makeuseof.com/tag/guide-best-budget-webcams-under-50/