I have no idea of prices in the area, or demand, so can't say whether it is good value or not. But even if I did, it is purely a 'private' decision between you and the landlord. If the site ticks all your boxes, then go for it.
But apart from cost, it seems like a logistics problem of timing.
How long will it take to find the job is permanent (who decides?).
Can you manage without the boat during this period.
Will you be able to find another mooring at a later date (at less cost?).
What is the deposit for. Is to hold the mooring pending your occupation for a fixed period.
When do you you start paying rent - and what notice to vacate is required - .
There are too many variables to ponder.
My simplistic approach is pay the deposit to reserve the site 'empty' (but probably paying rent from day 1) - until you know the job will be permanent. Then move your boat.
Meanwhile 'rent' the mooring temporarily (if you can) to a 'passing' boat.
