I'm full of man flu so I may have missed something here, sorry if I have?
I'm looking at this from a sideways stance, take a moment to think this thru...
Firstly ...how do you know your car needs this work? I'm assuming someone else has told you this, not the vendor?
But worst case: To be honest there isn't much here to break the bank, battery, roll bar links, brake pads, t/stat...the MAF is the dearest at £80. Remember it's an old car so it's not going to be 100%, if this the worst, well, most cars of this age will have some issues and wear, it's why they are cheaper than new ones, the best part of the car sounds good though...most of the parts you have highlighted are simply service items.
And...wow, that was one super cheap 156 at that price, at that age with those miles!
-New airflow meter...how do you know? It would drive very poorly from the word go.
-Need for a new battery: Remember that most 156's (as a lot of Italian cars) have a constant live feed to the stereo, it may not turn off with the ignition key out. You posted that you have a dodgy CD player that won't turn off...this will cause a flat battery flat overnight, a new battery will also go flat.
-Roll bar links and bushes, not expensive to fix but you would hear loud knocks and clunks on the test drive.
-Need for a new thermostat....why?
-Need for new breakpads....how worn?
-Also a full service and cambelt change due (possibly variator aswell)" known prior to sale...variator worn at this low miles is quite rare to be fair unless oil changes have been missed.
Hope this helps