We make big bale haylage and sell it, so offer the opposite perspective - just to give you an idea of why there are increases. Not having a go, because I respect that the OP is merely asking a question about costs.
The problem (for everyone) is that because of the shortage last year - mostly due to poor dry weather conditions, not a lot was made. It has meant that the stocks from the "previous" year which were available have been used up, so people are running low - farmers included. So demand increases and supply decreases. Add to that the massive increase in the cost of diesel for both farmers (to make it) and hauliers (to move it to the suppliers) and you have a market where costs increase. Don't forget, to make good quality haylage, it also needs to be fertilised. Fertiliser has gone up to somewhere in region of 3X the cost of last year - mostly due to the increase in diesel & production costs. Then you have the increase in wrapping costs - for horses, it is usually double wrapped - wrapping plastic has increased in cost due to the increase in the price in oil...
DH and I have been working out the costs for our haylage bales. We want to "make" between £18-£20 a (large) bale after costs. To make that, previously (early last winter), we were able to charge £24/bale off the field. This year, we have to charge £28/bale off the field - entirely due to increased costs.
Add to that the shortage of haylage and supply and demand - we are in South Wales and because of the lack of haylage/good quality hay in ESSEX, we have an Essex supplier coming to our area for haylage. He then has his haulage charges back to Essex on top of our costs...
Both our business manager and my DH have already heard of big bale haylage going for between £35 and £40 a bale in parts of the country and that is off the field. If you buy it from a supplier, they will add to those costs. Depending on how much you use, a way of trying to get it cheaper would be to try and buy it direct from a producer, rather than through a middleman.