Why offer anything up front?
Your ATPL's will take you at least 6 months, if you do ATPL's in 6 months you will not have time to do 100 hours in this period.
Do some flying before, keep yourself current during ATPL's - the "offer" is nothing special, it is a normal estimated price.
Remember if you need more ME, CPL or Night time, this will cost you more. Prices they have given are minimum required, rarely stays minimum.
How much they offer the IR for?
ATPL's books are normally supplied with the ATPL course, do they offer ground school or distance learning? This is also extra £'s! So if you have to do the ATPL somewhere else, they will normally supply you with all the books you require. You must follow an approved ATPL course.