Estimating number of beacons? Flutter SDK?

Is there a formula / algorithm to calculate how many beacons would be required to map a large-ish building (about 500’ long x 50’ wide x 4 stories)? I am trying to figure out if, at $33 per beacon, we should / can afford to use Estimote.

Also, is there a Flutter SDK available or in the works?

Thanks for any info.