Hi Sir,
I am a system engineer and i always love to work tricky system. i read carefully about your project details.
So, My solution is so simple, i created that solution for my UK client.
Solution: You have to buy a cloud VPS Linux server for lowest cost from China then i will create a opensourse great secure VPN tools in there and finally you will conncet to that VPN server from anywhere and unlimited users.
You dont neet to buy licence. Just you have to pay monthly few amount for VPS cloud computer.
I am waiting to hear from you for that solution !
Thanks