Best config and low cost in this case are mutually exclusive.
The best config would be to lease dedicated lines from your local telco provider. Pricing can be very high, but speed and reliability will be the very best. You might want to contact a local network services company to provide recommendations and consulting services.
The cheapest config would be to just get consumer Internet connections at each site and use a site-to-site VPN to connect all the offices to a single "central" office. There are lots of ways to do this, but it could be done for a few hundred dollars in equipment and probably $300-$400 per month in ISP charges. It would be slower and less reliable, but much cheaper - assuming down time doesn't cost you too much money.
Both solutions can be completely secure.
Running your own cable, or having someone do it for you is probably not possible.
--Russel