@Brian H. - I'm with both @Michael Wagner and @Scott Krone on this one. I would highly recommend buying one already in business. You can cut your teeth on the business side of things without much risk (if you lose a renter or two, it's not the end of the world). The trouble with development is that you don't get to make any money for 3-6 months (maybe more) while you build up the property. Remember, you also have to pay for things like pavement (or gravel) driveways, fences, gates, security, accounting software, website, lights, property taxes, insurance, and other things that don't make you any money while you work on renting it up. This is not for the faint of heart. If you have a deepish bankroll and want to give it a go, you could probably do it. At the end of the day, this isn't brain surgery, but remember, banks and investors want track record. The good news is that with buying a facility already in business, that serves as a track record.
I would recommend going the SBA financing route. It allows for a lot less money down (10-15%) and it reduces the banks obligation on the loan to about 50% of the property so they are a lot more interested in lending. They pretty much don't have any risk if they hold the first mortgage on 50% of the property value. There are more closing costs and a few stipulations but it also allows you to get 25 year amortization and the SBA portion of the loan (Bank funds 50%, SBA funds 40% and you fund 10%) is at a fixed rate. This is good news in a rising rate environment.
So, with that said, I think one of the best opportunities in Real Estate right now is buying mom and pop self storage facilities, getting them running efficiently and flipping them (or holding them).
You balked a little bit at the price of a facility near you ($600k). I will say that price, size, location (well location a little bit), nothing, matters as much as income to a facility's value. You almost can't do a seat of the pants with a facility because it varies so much. As long as the market supports it, I would say 85% is a pretty solid occupancy rate. I think many people use 7 SF/capita in a 3 mile radius as to whether more storage is needed in an area or not. Remember, that is an average for NY City as well as Green Bay, WI so you have to use some judgement with that number too.
I want to leave on this note: if you have the land already and you are looking to put up storage, I think this is a slam dunk (assuming the area needs it). You can put up buildings pretty cheaply and start small. But once you get into grading out a property to build a facility (I've done two 6 acre parcels now and it's cost me over $200k each just for dirt work and another $250K for paving) the up front pricing can get a little wild. With that said, if you have the property and you want to put up a bunch of storage, spend the money to talk with an engineer. They will be able to design the facility in phases and they will also be able to make sure you can handle the rain (and snow). This should not be taken lightly. It really needs to be thought through.
Good luck and feel free to private message me if you have additional questions.