Hi Gregg, thanks a zillion for the help.
Here's how I'm looking at my situation financially:
There's not much of a market for specialist bikes here in Ireland, but there is next door in England, so that's where I'd be buying. As usual, stuff is expensive there compared to the US (I had the same problem when I was buying a laptop). The cheapest proper expedition touring bike I've found is £900UK, or $1700.
I was chatting to some serious tourers on another forum, one who built his own bike and has cycled it practically everywhere on and off road, and he suggested I build it myself. He pointed me to some quality secondhand mountain bike frames on ebay, such as these:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ih=001&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=110094132979&rd=1&rd=1http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ih=011&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=320084380308&rd=1&rd=1I could pick something like one of those up quite cheaply, and then starting from there, I'd consider a final total of $1000 to be quite cheap compared to the other option.
Perhaps it's just a case that the kind of bike I'm looking for is a lot cheaper in the US, and hence the self-build option is cheaper here. It's appealing too because can get exactly what I want by building it myself.
Or perhaps I've got this totally wrong all together.
Thanks for all the suggestions, I'll have a look at the parts you mentioned.