Hi @spacey, thanks for your query. From the setup you describe, I would suggest you look at the Tobii Pro range of eye trackers.
The entry level product is the X2-30 who product page is @ https://www.tobiipro.com/product-listing/tobii-pro-x2-30/
This Tobii Pro range of trackers allow you to run eye tracking over a customised or non-standard stimulus size. You can read more about the particulars of this @ https://www.tobiipro.com/learn-and-support/learn/steps-in-an-eye-tracking-study/setup/using-the-x-configuration-tool/
As you mentioned, you would be conducting marketing studies, and such use is not permitted with the Tobii Tech Range of Trackers (4c, EyeX) without the purchase of a special licence and these trackers do not support multiple monitors or customised layouts.
For further information regarding pricing about Tobii Pro Products and services, please contact the sales team: https://www.tobiipro.com/contact/sales/
Any other questions, please let us know.