With the 25% discount that will be the same £15 as the other DLC, which is very reasonable price, so yes, OMG that is cheap, roll on thurs
Price/km is only one metric of value. You're also getting the Mk1 Coach, the Class 47 and Class 09 in addition to the route, where as the Rapid Transit DLC only comes with the Talent 2. The route, despite being short still has eleven unique stations/halts which is nearly as many the NEC (Thirteen). All the other routes are £24.99, so £19.99 seems about the right price relative to the other DLC routes.