i saw MR MDF quoted at over £100 a sheet , the normal timber merchant i use , it was £38 a sheet last year , then £90+ a few weeks ago and seems to vary quite a bit - TP have it much cheaper at the moment, I suspect its a mixture of availability , supply and possibly profiteering
I think i posted a while back on the issue.
I know builders are quoting without material, or the quote is only valid for a few days , OR as last week i had a discussion with a builder to provide a quote and he said , he can get the prices as next day or so , BUT that is likely to change when they do the job, this was for a brickwall