Are those prices plus VAT - always worth not forgetting.
A quick check of the internet suggest you you could do the same course with all fees in an almsot new DA42 for £3K or an Aztruk for £4K - both considerably better aircraft.
I would not recommend the 42 unless you are only going to fly 42s.
I think this boils down to why you are doing an MEP. If you are going to rent the same aircraft afterwards (because that is all that is conveniently available) or because it is the only convenient aircraft at your local school then in my book convenience will win every time. I would not be driving an hour each way to fly a different aircraft - but others might.
If on the other hand your local airport has better twins to rent, and that is what you intend to do, you should train on the aircraft you intend to rent if at all possible.
6 hours is not a lot of time behind the wheel of a proper twin (like the Aztec). You will need time to be comfortable so you are far better staying with what you know for the first twenty hours or so.
You mention there is not a lot around in terms of other Senecas. Do you mean other twins as well or is there some reason you want to train on a Seneca?
In summary I dont think they are bargain basement prices but they are a little cheaper than most which doubtless reflects the aircraft being used.
However am afraid when it comes to fly twins forget the odd hundred here or there, you need to count in thousands.