Once the fibre (if you don't buy junk) is in the ground upgrading becomes very very cheap. And given that the required access speeds aren't very high (100M-1G),

Once the fibre (if you don't buy junk) is in the ground upgrading becomes very very cheap. And given that the required access speeds aren't very high (100M-1G), they can be had rather cheaply second hand/new. So you can direct all the money from the cost savings to upgrading your backbone, where it does get rather expensive.