BT Reconnection Charge is normally £124.99
Reconnecting to BT is always at least a 12 month contract.
If your existing suppliers uses full LLU (removed completely from BT network) then BT dont normally charge to reconnect as long as the line is working when you ask BT to take it over.
If it is a stopped LLU then BT would charge to reconnect as an engineer is required.
Their is currently a £29.99 reconnection/connection offer available subject to 18 month contract and a minimum call requirement.
http://www.productsandservices.bt.com/consumerProducts/dynamicmodules/pagecontentfooter/pageContentFooterPopup.jsp?pagecontentfooter_popupid=24641 
