I'd check out the local colleges. I wandered into the fitness center at our little community college and found two 4' stacks of brand new mats sitting in the corner. It didn't look like they'd been used much and it broke my heart to see them sitting there not doing anything
Check with the college activities office to see about the possiblity of starting an aikido club...especially if the have space and mats you could use for free.
I have a friend who teaches tai chi at a University. He has it set up so Uni. students get credit and non-Uni. people pay some ridiculously low fee....something like $15/month.
Gymnastics schools will have mats and may have some open time in there schedule they are looking to fill.
I would definitely start small. The place I teach at started at the local Y and moved later. When my sensei started teaching it was through the local Community Continuing Education program. If there's a way you can gather a student base while keeping the outlay of cash low I'd go for that first. Once you have a solid core of students you can start looking for your own place....or stay if you like it.