Easy answer is that video eCPMs could range from anywhere from $10 to $50 or even higher.

Short answer is you can charge as much as you can get away with

Long answer follows

# of visitors is ideally not a metric to benchmark what you should charge. The two primary factors being,

1) Audience Attributes - Assuming you are able to tap into specific public areas, you could segment your pricing based on that. Public areas near big retail stores, dense banking areas etc. suggest that your audience could be more affluent so you can seek high CPMs from brands to show ads in those areas

2) Advertising Objective: You mention a 30 sec non-skippable video ad so not a lot of scope here beyond awareness/consideration but could you potentially bake in a direct response format (say a coupon code for anytime within 1 mile of a Target store). Now if you can prove direct attribution of sales from ads on your platform, it opens up a far more lucrative pricing option where you could charge not only for showing ads but potentially a cut in sales