It sounds like a fairly "normal" price from what I can tell. I've paid for the content of a "navel" bottle from BOC and that was pretty spot on £70. I have also paid for a "crotch" bottle from Energas for pretty much the same price as "M1CDQ". The Energas representant said, when I mentioned I had the "navel" bottle, that "You'll probably need two of these to one of those". I.e they're not filled to the same level and obviously the size is different.
If you buy one of these bottles of Argon for £70, let's say the bottle rental might be about another £30, so the gas will end up costing you about £100. Perhaps more. Perhaps all plus VAT, too.