It would be dependent on the type - some Biz TR providers are happy to work when you can and others a little more demanding. In house for an airline I have no experience of, but I would expect the shortage of TRIs or LTCs might mean a demand once frowned upon is now welcomed.
Like most instructions positions - you can mostly ask for x and get it from what i’ve heard.
If if you have ME CRI and IRI and happy to lower yourself then a “pottering” contractor can easily get £70-80 per hour with no commitment or fixed roster with one of the major training providers - some insist on FI rather than CRI if they’re integrated.
A friend of mine who drives a Challenger RHS has had numerous calls to sandbag in various locations and the money was OK. Limited or no commitment again - just depends on more specifics of type and location.