E90 320d Clutch Repair

The gearbox in my 2006 320d has gotten very stiff over the past few months, to the point where 2nd to 3rd gear is very rough. The higher gear changes are smooth, and reverse is ok too. I changed the gearbox oil but didn't really improve it. There's no vibration in the clutch pedal, so I'm wondering is it a gearbox or clutch issue?

Anyone any idea how much a clutch/DMF change costs in an Indie garage? I'm trying to weigh up if it's worth spending the money to get it fixed or to trade it in?

Thanks!