Dealership had advertised half off MSRP on a huge banner outside there business where interstate drivers can view. They told me it was on the lease p

Dealership had advertised half off MSRP on a huge banner outside there business where interstate drivers can view. They told me it was on the lease program which was fine with me afterall it was half off the MSRP. Well after six hours in the dealership in negotiating a payment that is suitable and decent amount on my trade , I came to find out that , you have to pay the other half of the MSRP to own the vehicle. That is not half off MSRP. This is very misleading and I consider it false advertisement. Is this worth pursuing with legal letters or other legal actions?