Seems to me that you c0uld get a VECTOR CONTROL specialist from your city or state Health agency to give you free consulting , and, Armed with this information, you could develop an actual work statement to present to a "Verminator".(Too much ambiguity always yields outta sight bids)
The biggest problems in getting rid of rats is to get rid of the trash and areas that they like to dwell. Then, keeping foodstuffs away from them while the poisoning events occur is another step that requires coordination and cooperation from the residents. If just one guy doesnt do his or her part, all the rats will take refuge in that guys place and just tred water till the verminators gone.
The best poisons have been banned for several decades now so were left with stuff like Warfarin (which is relatively safe around pets because the pets will puke it up if they eat it) Rats cant puke so thats why these anticoagulant poisons work well and they dont develop any immunities to pass down to their ratty heirs. However, they do have some problems .
The reason Im sounding like I know what Im talking about is because I opened an office in Santa Fe about 20 years ago and it was rat infested. We also got a couple of "sticker shock" estimates so I called in the State guys and even a tribal vector control guy because we were working with the NAtions. We saved boucoup bucks by essentially taking responsibility on ourselves. The biggest thing was the cleanup and removal of ratty cover.
Is the bid that you mentioned inclusive of all site cleanup as well? If its just poisoning, the rats will soon be back no matter how much follow up is done. Rats will press their burgeoning population from elsewhere and the bastards will take over what appears to be a freshly de ratted niche.
What does the 270K get ya? if I may be bold to ask