I’ve looked at some gas setups for large farm greenhouses, but if you are just considering a small greenhouse it’s a lot more reasonable. The heat is pretty dry (about 30-40% humidity) so you would need to consider that. Depending on the number of machines you want will define your setup costs. There are a few greenhouse miners out there you could reference; Scandinavia I believe.
That said, do you have an idea of the number of miners you might employ, or at least, the desired BTU output?