Over £400 I'm afraid.
The reasons are that the price of an inlet cam timing variator is up to £80+vat (you'll more than likely need this to ensure the engine dosen't sound like a diesel. Variators become noisy when worn, but don't do engine damage.)
The 2 litre has a more expensive belt tensioner than the 1.6 or 1.8 engines. It also has a balance shaft belt and tensioner.
It will take about 4 hours to do all of the above, some garages may be a little quicker, but count on being invoiced for 4 hours.
You may also require new cam cover gaskets which although cheap, add to the overall cost.
You'll be better off finding a specialist rather than a dealer. I'm also surpised to find a twinspark about to get its 1st belt at 70k. I had a 146 come into the workshop recently, and the dealer had just done the 1st belt change at 72k. I think it suggests dealers still aren't paying enough attention to the belt issue.
these engines do have a habit of breaking or stripping teeth from timing belts.
The general concensus is to change the belts and tensioners every 40k. I know its more expensive, but if the timing belt breaks, you won't get change from £1500
I know it sounds bad news, but I would personally change the belt and tensioner every 40k, and then at 80k change everything- variator included- as a routine. That way I think it gives decent piece of mind without being unduly expensive.
Other than that, I hope you've being enjoying your 147!