Prices vary spectacularily all arond the country, and from business to business, which is teh competition part, of it which is fair enough, but what you will also find, even on mundane service parts many add what i refer to as a "Scene Tax" Wherby ANY part, accessory, panel, or item will have a noticeable mark up as the seller belive we are stupid!!!
As we are all part of the VW gang, that in T1 terms [no offense to any T1 driver mind] i just beleive they have set the benchmark for ridiculious prices where a tatty T1 is worth well in excess of a really smart well made T4, which i find incredible and where T3 prices are starting to get really really silly now.....even T4's are getting crazy price wise as many find it as the next T1-T3 it will not be long until T4's also price themselves out the market to most, at which point T5's will be more appealing and so on and so forth, we can well complain all we want but the sad truth is that we the owners and enthusiasts cause these issues by very very often pay far to much for what is essentially a VAN, which has a knock on effect with their parts obviously....
When it comes to mechanical parts, especially with 1.9's i have often found searching for the lesser VW marques parts i.e Skoda, Seat and often even Audi's can pay dividends in terms of costs over aftermarket steepy priced copies, so the best advice after all that is to compare the market always when seeking any part for your bus, as often cheaper alternatives are available, which can often save you a fortune...
The only place i will never compromise is when servicing my bus i always without fail fit VW parts [filters,cambelts, waterpumps] and such like as it is well proven it is false economy to do anything else, apart from that good brakes, tyres and steering and you will have a bus that will be dependable, start, drive and be enjoyable to own for many years to come, and save you a fortune on parts to boot..
