I'd just go day-rate, probably $400/day, nix the $1500 retainer, because if it was me I'd go find someone else. Now if they only paid you say $100-200/day with the retainer, then it might balance out.

Hourly rate could also be something of $40-50/hr flight, $20-30/hr standby if you so desire.

If you'd base it off a straight yearly salary(which some people don't want to do, but honestly could be cheaper for them), I'd say $35,000 for starters, maybe up to $40k first year depending on the actual amount of work you do.(think avg 7days/mo @ $400=$33k/yr, 10days/mo=$48k). If you can pick up some other contract work out there, and have plenty of "heads-up" time then you would have a pretty sweet deal going, contract would be the way to go and really earn a lot of extra money without the obligation.

I'm just going off what I would want to be paid in your position and experience. Also, what geographic area are you in? Some places, those rates could be too high, and a few others it might be way low. If you could find out what some 400-series Cessna drivers are getting, I'd say that'd be a fairly good starting point. Good luck!!!!