I have no clue about this topic and this comment isn't representative of my employer whatsoever, but... Since you've never experienced this with other domains, does the word cheap have to do with it? When I think domains, "cheap" instantly reminds me of those early quasi-legal online pharmacies and if I see it in an email almost certainly it's spam of one sort of another. I could see being problematic in spam filters…
Cheap is just the everyday word for low cost. It can also mean low quality, but that connotation depends more on context.
Besides, there are many other successful companies with "cheap" in their domain names.