They are about $100-120. You can get them in the bolt-on or weld-on form. You are fine on your clearance. They are flush with the body. You can get them at many places but I got mine at mustangsunlimited.com for $120(weld-on).They will just put a connecting bar(s) to your two rails for less flex to the body for a longer lasting mustang.
(Also improves your cornering)Hope it Helps!!!!!!