Aruba for small environment (4-8 AP), AP and management choices

I'm currently trying to inform myself about the options regarding for following environment:

Two story concrete building (each level 250m²) with a large open garage on the ground level (700m²). Maybe I can get away with 4-8 APs.
Usually low people count and throughput. Will need two wireless networks (internal and guest). Wifi roaming required, should be a simple, low cost and maintenance solution.

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So I came across Aruba APs, which seem not that bad. But I'm still having a hard time wrapping my head around it.

• seems they have controller and cloud based APs, or with internal and external controller (RAP/IAP)
• what's the lowest cost, possibly without cloud solution?
• Are their wifi software controllers freely available or is there any free/open source alternative? (?Aruba Mobility Controller/ArubaOS)

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Ubiquity is also an option, but I'd like to get a rought overview about the market.