There seem some fundamentals here, applicable to rail, bus, whatever.
A premium of just 25% sounds unrealistic.
If the employees won't work at weekends (or nights, or earlies, or strike days, or whatever you cannot staff reliably) in these conditions of pay and experiences, then you just schedule appropriately and realistically, including closing whole services for the weekend. If the staff are not available, and the services are regularly and constantly cancelled, then any remaining passengers will stop coming anyway. Notably, this last week I travelled Weymouth to Waterloo. There were ... three in the carriage, not just leaving Weymouth, but arriving at Waterloo as well, at 5pm on a weekday. The parallel roads are packed at that time.
If all this is the case then you stop pretending, to politicians and others, that the railway/bus/whatever is, and ever can be, somehow a complete substitute for using your own car, which is typically readily available 24x7. For those without a car ... tough bananas.
You stop wasting money on capital investments, like HS2, which is supposedly to have operations managed by Avanti or their close successor, if the workforce to provide the service anticipated is not going to exist.