Tyre rim refurbishment?

[sproutdreamer]

I have a tyre that loses a little pressure over time. My wifes car, I would just top up the tyre pressures when I put in petrol for her about once per month so needed sorting but no rush. However my daughter is now using her car and has not checked the tyre pressures for 3 months so down to about 10PSI. I have checked with soapy water but no signs of a slow leak so my assumption is that the rim is not seating too well and in use is spilling a little air?

What should garages normally charge to take off a tyre, clean up the rim seating inside refit and balance a tyre?

[Madasafish]

£10 here. excluding balancing.