Building rules can cost more than the wash
Before you optimise the wash price, check the rule that can dwarf it. Most managed towers and many gated communities regulate washing in their parking: some ban it outright, some allow only companies registered with the owners association, and some allow any waterless or steam operator as long as no water reaches the floor. Violations are typically enforced against the resident, not the washer, and fines commonly run well above the AED 30–120 you were trying to spend.
Have a two-minute conversation with building management before your first booking. Ask three things: is mobile washing permitted in the parking area at all, does the operator need to be pre-approved or sign in with a trade licence, and is steam equipment allowed — some buildings object to machines plugged into common-area sockets, which is why good vendors bring battery-powered units. The questions double as a quality filter: a vendor who asks unprompted which building you are in and what its rules are has done tower work long enough to price it correctly.