Ciao. What I think you actually need is a different development team. If they can't handle security and rely on an outsider to check it for them, then they're either not experienced enough, either not sure on their skills (on this kind of job), but they are certainly not reliable. This is how I see things.
But, if you're on a budget and don't want to spend too much on development, I can agree using a cheaper and less experienced team, but you should know that your expectations have lower chances to be met.
Let's have a chat and get into more details. Chatting is always free.