I suspect YHA in Dolgellau want their money early, hence the timeline. Multiply £42 x 200 and you get in excess of 8 grand budget... some of it will need to be spent well in advance. It's different whether you have to commit a couple of hundred or 5 grand
Re. Paypal, again, they charge a fee in line with the market... I think it's 4% of the transaction... so on 8 grand that works out at 320 pounds, which is probably not a million miles off the budget require to stock a control. Cheques + stamps cost nothing, only manpower, which is done for free...
Moral, with a cheque you get 4% more fun for your money.
Being a bit OCD, I did enjoy assembling on the bits and posting them... there is something satisfying that pressing a key on a computer cannot replicate, but maybe it is just me...