A green house/hoophouse can be built relatively inexpensively. A recent calculation arrived at $6000 to build a 20'x48' poly house, including the necessary containers and planting medium to fill it. A 960 sq.ft. area can yield between 10-20,000 plants at $.50-3.00 per plant depending on the container size, that's a range of $5,000 - $60,000. Lets make a conservative speculation that one green house can generate $10,000. If successful the house will have paid for itself and made $4,000 in profit in one season. The house would make larger profits in subsequent years, without the initial cost of building the structure.
The greenhouse funding model
Curtis Stone an urban farmer in British Columbia has perfected a model for growing food on leased and borrowed land. He is apparently able to generate $75,000 on a third of an acre producing vegetables and leafy greens. It's an interesting model that might be used to inspire thinking about underutilized empty lots in Granite City. Of course, producing fresh vegetables in a city known for heavy industry is probably not the best concept but if the focus were growing native plants for brownfield remediation and habitat restoration perhaps there is a kind of urban agriculture that makes sense for Granite City.
Gateway Greening is a gardening organization in st. louis that promotes garden making and education, administers an urban farm, coordinates volunteers and have a dedicated staff. Their focus is primarily food and they unfortunately do not work in Illinois. Nevertheless they serve as a potential archetype for an organization in Illinois focusing on native plants.