If you are only lock out of 1/2 and reverse but can go in other gears, there is a problem with the transmission.
It's weird that they have the flywheel cheaper than the clutch kit.
replacing the flywheel when you install a new clutch is better, because you can't resurface a dual mass flywheel. I don't think they would take the risk of changing the clutch only.
For the transmission, just ask them.