Christopher Kunz has shared about a resource he came across that offers complete PHP encoding for a much lower price than some of the other services - phpshield.com. It seems a little too good to be true, though:

However, the phpShield.com home page did not offer the slightest clue who actually is behind that product. [...] It's common practice to whitelabel your solutions and sell them under different brands with different feature sets to different target audiences. However, we always clearly state who is behind the whitelabelled solution.

A little more digging shows an interesting relationship between the company that sells SourceGuardian and the company behind this PHPShield (Inovica). He sees the deception counting against the company and has just "struck one off the list" from his search for encoding methods.