In the past if you were joining without being type rated, you would be expected to join the Channex Type Rating Scheme.
In short you had to pay 20K for 737 or 17K for 757 upfront.
Jet2 would then divide your salary into 2 parts for 3 years - CTRS salary and Training cost repayment. The Training cost repayment part would be tax free. After 3 years both parts are combined to make full/final salary and taxed.
As for mil types, I would think it depends how badly they want/need the job. Jet2 are pretty good at dangling the carrot.