Hello there Andy,
I can offer you a very cheap but at the same time a very good security check with a list of bugs/issues.
Many users on here have used me in the past to find bug/security issues and im sure some will tell you i do a very good job.
I have also been thanked/rewarded by Apple, cnet, talk talk for security finds.
Note: I am not a coder i am a just a bug/security finder, but my brother is a coder and could help you with this.
If you want more info inbox me and i will do my best to help you.