What do you supposes the actual cost of a Housing Ward is for Square Enix

[Shibi]

Fixed DC costs are about $6100 per month per rack for tier 1. This is floor space, security, fire suppression
Maintenance costs are about $5000 per month on top per rack - this is power, UPS, Cooling, Generator, data (a huge ongoing cost)
Soft costs (labour) are about $4500 per month on top of that per rack

So, maybe $16000/month for 21 servers in a tier one DC. (servers not worlds... each world needs many servers - from the photos we've seen Materia's 5 worlds had 60 servers at least)

if the option was actually made to players to make a one time payment $10-$20 for a guaranteed plot which I suspect is WAY more then the actual cost for Square Enix

You'd be surprised at how those ongoing costs for power, cooling, maintenance, security, fire, diesel, staff, and so on add up.