I would think the GH is going to be your biggest up-front cost and prices on them, fully equipped, range from $5000 for a small hobby type to $250,000 and up for pro/commercial sizes depending on the size you want and the materials it is constructed from. Once constructed then you have the annual overhead costs of heating and cooling, electrical power, water, etc.

On the other hand you can till a garden, amend it well with high quality compost, and grow plenty of food for a family for just the cost of the tilling, some compost, some seeds, and water - under $100 depending on size you want.

Lots of research available online on all the aspects.

Dave

To piggy back on what Dave said, it is also pretty easy to grow enough food so that you have fresh veggies year round either by storing them or growing the hardy ones under some winter cover. It's easy and cheap to throw a low tunnel over some spinach, kale, and other hardy greens and eat from it all winter. And grow sprouts in your kitchen in winter. You don't actually need a green house. Add a little canning and freezing to the mix and you'll have your own year round fruit as well (after a few years for trees/vines/canes to become established). You'd hardly ever have to drive the 2 hours to the store.

If you have not seen, or read, Elliot Coleman's "The Four Season Garden" you might want to get a copy.
You may also have a chapter of SCORE nearby with people that can help with a business plant.