How much of the value of the company is tied up in it's technology?

Your leverage at the moment is, if you decided to get another job, you would walk away taking all knowledge of the current system with you. Imagine you quit, and something went wrong the next day - how long would it take them to fix it?

I think your boss did you a huge favor, taking a risk on you this first year. Now you are no longer an unproved dropout, he owes you a real wage. Keep both of those in mind.