Hay rolls are exactly that: hay rolled up just like a jelly roll. These can be unrolled, but after time and the start of some decay, it may not be so easy. These rolls weigh around 800 pounds dry. If they have slurped up some moisture and flattened out, you might want to skip trying to unroll the things. If you are looking for good hay in the center, this would be a simple way to get to it.
I would suggest that as soon as you have them in a desired location you cut and remove the wrap, be it plastic mesh or twine. Once decomposition gets going, it will be a struggle trying to untangle and remove it.
You have 40 of these bales, figure 32k pounds of hay. Various sources list hay the CN ratio of hay anywhere from 25:1 (I'm guessing for fresh) up to 90:1. After a year and a half, with some molding, I'd say the N in the hay is probably already consumed or dissipated. It's a pretty good bet that the hay will need at least some green material added to get it composting. On the high side, you may need as much as twice the weight in green material to get the CN ratio to an optimum level. For this sort of volume, windrows and a
bucket loader can make quick work of the task. If you already have a few yards of compost available, it would do wonders if you area able to blend it with the hay and the green material you add. The purpose here is to inoculate the windrow with microbes to give it a head start. If you don't add it, the
project will take a little longer is all. Compost happens.
That's if you want to play by the rules.
Left alone, the hay will slowly decompose.
Mice and bugs will move in, the rolls will sag, maybe sprout some weeds, but for the most part they will stay right where they are for a while. If you can secure a source of greens in great volume to add to the hay, you can process the whole load all at once. Some machinery would make things easier on your back! If you can't process the entire load all at once, that's no problem either. Draw from the hay as needed to provide the brown material to balance what green material you have available (I'm thinking goat manure).
Using the hay as a mulch around garden plants is a fine use. As the hay decays it will add to the humus around your plants. This is a very common use for spent hay. How big is your garden? This use would not help you to produce a marketable product. It would eventually be incorporated into the soil in the growing area.
It's shoot from the hip month...
What you are describing is a humus farm operation. You want to make lots of compost and sell it. It's a noble endeavor, and the market for the product is growing.
The packaging plan can use some attention. If you are referring to plastic bags, they are not particularly strong. 40 pound plastic sacks can be had at the big box stores for a couple bucks, maybe 4-5 bucks for the premium quality Black Cow brand. If you are referring to the tougher paper lawn and leaf bags, they will probably take more weight, but I think the cost may make them impractical.
I have purchased compost in bags, but buying it by the cubic yard was cheaper. When I got a utility trailer I could handle a load much easier. Now I give a guy 50 bucks to drop off a load in a dump truck. When I bought it buy the yard, I was able to measure the volume. It took me about 50-5 gallon buckets to unload the utility trailer. The math says it
should take just over 40-5 gallon buckets, but there is always some fluffing during the work. Prices for a cubic yard of compost have ranged from $18 to $33. That works out to $0.50-$.82 per bucket. Would it be practical for your customers to bring their own 5 gallon buckets? They can pack em down and pay a buck a bucket. This method has no packaging expense.
When I bought a cubic yard, the seller would load my trailer or truck with a 1 cuyd bucket loader or skid steer. 1 cuyd of compost weighs somewhere around 1000 pounds, depending on who you ask and how wet the material is. Those little trucks can only haul about 500 pounds before the start to have suspension troubles. If you don't have a bucket loader or a means of weighing a truck, the 5 gallon buckets can give you portion control. Give em 40 buckets, fill and dump.
I'm concerned about the price you paid. Around here, a fresh round bale runs me $30-40. Spent hay can be had for the taking. Loading and 15 mile delivery for a dozen spent bales would be on the order of a hundred bucks. Pretty much it's just to pay the driver and fuel. The product has little commodity value. If you keep going with this project, I think you'll be able to get feedstock for a much better price.