Depends what type you want, some Altro types are cheaper than others. I've recently emailed a couple of companies regarding a 2m x 2m piece of D25 Altro to replace a damaged area in my van and they both came back at around £90 which I thought was a bit pricey. There is a company on the Bay who do off cuts/end of roll pieces for much less.
I bought a bit ready cut for a T5 for around £70 (not the ebay company) less than a year ago. Can dig out the company for you if required, it did save a load of hassle cutting it.