Insulating an older pole barn

[HoosierMark]

I have an 24 x24 pole barn with concrete floor. It looks like they used 1inch foil covered foam before they put the metal on. I want to insulate it enough so I can heat it to 40 degrees to keep my paint and liquids from freezing. It is a storage building at a rental property. I just need to keep it above freezing cheaply. The building has 6 x6 posts set 8 foot apart and 2x4 s horizontally every 2 foot. Trusses are 8 foot on center.
I first thought of fiberglass insulation between the 2x4s then thought maybe 1.5 inch styrofoam between the 2bys. Considered studding it up but just want to control temperature to store things.
We have lights below the trusses so I am thinking of laying some 2bys on top of bottom chord of truss and just laying fiberglass rolled insulation over them.
Any tricks out there I should use? Easier ways to accomplish my purpose?

 

[stm317]

Insulation will slow heat transfer, but it's probably not going to keep a building above or below a specific temperature. Especially during an extended streak of cold weather like we've had recently. Even a well insulated building will allow temps within to drop if the outdoor temps stay low enough for long enough.
Walls:
I live in your region, and decided it was worth it to use 1.5 inch foam panels between the girts on mine before I insulate any further. I plan to eventually stud it out and insulate with R19 fiberglass rolls, but the foam does a decent job for now, and doesn't take up any room in the building. It will only help things long term. If you want maximum R value for as little money/effort as you can, they make thick fiberglass blankets that you could hang between poles and avoid the cost of framing. Going this route would limit your ability to hang things from walls though.
Ceiling:
That being said, most heat loss will go through the roof. Insulating the ceiling heavily will be required. You're near the border of climate zones 4 and 5, which recommends R38-R60 in the ceiling. If you won't be heating this shop, I'd target that R60 value to minimize heat loss. Blown cellulose is usually the most cost effective way to get high R values in a ceiling/attic space. That would be something around 15" of cellulose. Don't forget a vapor barrier below the insulation.

 

[HoosierMark]

Maybe I was not clear. I plan to have some type of heat source in the building, I just want to minimize the cost of the fuel. I realize that it is a small space, will be closed up for days and will only be heated to slightly above freezing. So my fuel cost, will be minimal in general. That is one reason I need to balance out cost of insulation with cost of fuel. I figure there will be about 4 months that I will need any heat at all. If you spend $500 to insulate the space and it only saves you $50 per year, it may not be cost effective at this point. In 10 years they may have a cheaper way to heat it or my use of the building may have changed.

 

[stm317]

You said that, and I completely missed that part. It's just going to be a math problem then based on pricing. I'd still focus on the ceiling first. That's going to provide the biggest benefit.

 

[Perrorojo]

I bought one of those spray foam kits online and sprayed the ceiling. Total mess and very difficult to do correctly. It did help tremendously versus the fiberglass bat that was originally there. We're a little colder than you are but I would do the 3" Polyiso hard board insulation and then sprayfoam any gaps.