Okay....
Cost new is £3850 - too much IMHO, so got mine secondhand. You can get them for £2500+ that way, much better value for money. There isn't much that goes wrong on them with the exception of cells - which you should replace as a matter of course anyway.
Training for the Mod1 course is typically £500 in the UK- for instructors look at
http://www.ambientpressurediving.com/Frmsetinstrs.html - there's even one in your neck of the woods. I strongly recommend doing the course- you can't buy one new without it and if you buy one S/H without doing the course and you don't have your shit together and know EXACTLY how it works it will kill you, no question. Apart from anything else, a decent instructor will give you lots of hints and tips that aren't in the manuals (sadly deficient in some respects as Ammers will be happy to tell you)
The physics and physiology is not rocket science, but the way it operates and how you dive it is very different from OC.
Cost wise, once you've got the thing it's swings and roundabouts. If you do lots and lots of extended duration dives 30m+, it works out a lot cheaper than OC to run ( if you dive trimix it's MASSIVELY cheaper) - my gas bills on a recent Scapa trip were less than half of the OC boys on the boat, and that was typically 35m-odd diving, but I was shelling out appx £7 per 3 hours in the water for sofnolime. This is based on APD's recommendations on scrubber life bearing in mind worst case scenarios in terms of temperature/workload etc. In warm water and with a low workload, scrubber life can be a lot more than 3hrs, but it's a judgement call as to whether you want to take the risk - I don't, it's only money & I've only got the one life.
Basically, it's not about cost. It is difficult to justify the considerable expenditure it costs to buy and get trained on the unit compared to OC purely on a financial basis. However, the difference it makes to your diving (and enjoyment of same) is colossal. 1 hour at 30m? No problem, tons of gas. Same at 40m. Same at 50m. The question is, how much deco do you want to do and how many bailout bottles are you prepared to carry in case you flood the loop? Want to see lots of life - up close? No problem. Not having any bubbles to deafen them means the fish come right up to you, and you can sneak up on lobsters a treat.
Typically, I'm in the water for a minimum of 90mins including deco every dive, and max Diluent/O2 useage has been 80bar from each 3l. 80bar is actually quite a heavy consumption for one dive, but I like to practise drills when I'm down there which uses a bit more gas.
On-going costs - £55 per O2 cell, so multiply that by 3 + 1 spare. They're supposed to last 18-24 months, but it is much less aggro to change them every 12 months. The spare will last longer if it's left in its sealed bag.
Batteries - £2.30 each and last for 35hrs on the Master controller and 70hrs on the slave, so negligible.
Gas - negligible, typically £10 for a hard weekend's diving.
Sofnolime - £50-odd for 20kg drum.
Servicing - negligible. It uses two Apeks first stages - the O2 side has a lower IP than normal, but that's the only difference - so pretty much what you'd expect to pay on OC.
The rest of it you do yourself - O-rings, scrims etc - I don't have the prices handy, but they're also cheap.
Had mine just over a year now, 100+ dives on it 30-50m, can't see me ever diving OC again.
Rob