Commercial Roof top air handler cleaning

I do alot of cleaning for our local hospital
They called me and asked to talk with me. So I go and they want to know if I could clean the inside of the huge air handlers on roof and in mezzanine floor. They are behind and need help and want me to probably do them all every year there are over 30
The process is not that hard and they will give me one of there guys to show me what to do
These units you actually go inside of and they have doors to access coils and filters
Have to electric pressure wash coils and walls and vacuum water back up
Clean glass window in doors
Wipe down dust areas pretty much clean it up good
And change all filters. There are alot
He said it should take 3 hours or so per unit
My question is what the hell do I charge.
I don’t have to ever bid on jobs for them as I am the only one they use
I normally give them a price when they request service then they issue a P.O number and I go to work
I know we can handle the cleaning of. These just not sure what to charge
I try to stay kind of fair so they keep me yet they probaly pay more than most my accounts
Any one ever do this type of cleaning
Just looking some advice on pricing

My thinking if it takes 3 hours and they supply chemical I’m thinking somewhere between 200 to 250 per unit. Let me know what you thinking

Sent from my SAMSUNG-SM-N900A using Pressure Washing Resource mobile app

This is a link to a diagram but these have walls around them you go inside unit

Sent from my SAMSUNG-SM-N900A using Pressure Washing Resource mobile app

If you are using an electric power washer your operating costs will be a good bit lower than a truckmount, also with them supplying chems you are mostly looking at labor. AND you aren’t coming in as the expert (since they provide training), so it would be hard to justify a premium rate. Your price sounds pretty good. Maybe offer $200 per with a signed maintenance account for all 30 handlers annually, or $250 per if its as needed.