I'm also on the fence about this. I'm also self-employed but for web stuff and every once in a while I get friends asking for favours. Nope, I don't even roll out of bed for anything below 1,500 – 2,000, sorry. Otherwise people don't tend to take it seriously and drag the project on.
If you flip the perspective around, he could possibly see this as a way to test how serious you are about following concepts:
-> Boundaries in a relationship & respect of each other's professions: If you're willing to pay him for his time, he may see that as a form of respecting him for what he does instead of just taking advantage of him. Also this could be about you respecting his time on the weekends.
-> Financial responsibilities: Similar to above in that you're willing to pay for good quality.
If I were you, I would go get another round of quotes from people and see what different companies say. Then with one of those other companies, work out a payment plan of 3 payments over the course of 4 –6 weeks or so.
I would remove this from the relationship entirely. You could tell him that you changed your mind and wanted to have it done really quickly without having to partially DIY this time around. Add something about wanting to respect his weekends, yada yada, etc.
After that? I'd stop doing certain tasks for him and pull back on those, especially if he isn't monetarily contributing to some of the meals you're cooking or his sister didn't pay you for petrol for the ride, etc.