L322 Transmission Slip

[L1OFF]

I have a 2007 TDV8 3.6, the transmission has on a couple of occasions lost all drive forward or reverse (no fault on dash display), after a few minutes stopped with ignition off its back again. The transmission oil, filter etc was changed in 2016 so I'm guessing its not an oil problem. I'm planning on getting my local garage to check oil level just in case. If (as probably likely) I'm probably looking at a reconditioned box, what sort of ballpark cost am I looking at?

[L1OFF]

Update

Yep low on transmission fluid. Only 3 Ltrs came out.