Guys, there will be no recruitment onto 757 at TOM. The fleet is contracting as old 757s are replaced with new 737NGs. The plan is to have a fleet of 787/737NG and around 10 or so 757s until the end of this decade. People are regularly directed off the 757 onto the 737, so they'll be no new recruitment onto any fleet but the 737NG.
The £7000 is taken off salary at source, so you won't pay it out of your net income. So the real "net" cost to you as £4,080, spread over 12 months.
The £7000 is to pay for your Operator conversion course (3 weeks of ground school and sim) and the costs associated with your line training (effectively the safety pilot for the first few sectors and the check capt on your final line check).