The good news is that SharePoint Internet Sites (previously around £10K) is scrapped so you can publish your site and subsites directly to the internet for free!

Just licence this SharePoint Server on each server installation (only one is required – contact us if you are unsure of spreading your services and applications across virtual or physical servers for failover and speed). Then licence each of your Users or Devices with Standard CALs to access any of these distributed services. Add Enterprise licences to those Standard ones for users who need the additional enterprise functions (see here).

Note if you don't already have SQL Server licencing and need more than the free SQL Server Express edition (yes, it works fine with SharePoint!) then you can keep costs down by using the Per-Processor licence version.