The club have said that 750k was "way off the mark"
And it has also been said that there wil be installments depending on performance
Remember, the Brighton Argus said Albion pulled out when Swindon asked for 700k - so I don't think 750 is way off the mark at all.
By the way, nobody at the club at all said it was 'way off the mark' (as you have quoted) - that was actually the Adver, which did not have a direct quote.
I refer you to this text:
The fee was undisclosed although reports quoting £750,000 are believed to be well wide of the mark.
.. which is clearly not direct from the club in any way, shape or form.