Commercial Help

I need help bidding this old house turned business. They asked for exterior only with the occasional interior clean of only the walls of glass. They want twice a month and possibly weekly. These windows are old except for the 3 walls of glass that they have. I tried putting my usual business quoting formula but only came to $75. I dont think that would be right since there is a lot of glass and tall glass at that. The management is also fine with using a wfp which i plan to do. The TDS is only 30 so that should be easy. I figured I could quote it like a normal residential clean and then use a percent of that to work up weekely and bi-weekly quotes.

What do you guys think?