First tip is never bid to get it. You need to figure out your cost and what profit you want. Be confident in what you want.
Do you do similar size properties to one single unit? Say 10 min x 33 units = 5.5 hours. The take your normal drive time 3 min x 32 = 1.6 hours saved. So might figure 4 hours for job. Just a vague example of how I would bid the job although I do not know the size of property, equip type, or number of employees.
What if you bid it at 15 because "you really want it" and it turns out it cost you 17 per unit to cover labor, operation cost?