No experience of torque converter swap costs as said, but to give an idea, ar 35 boxes change hands on here for 50 to £100 I believe, add to that fitting costs. My experience shows removing and re fitting an auto box in order to change a crank seal can be done for £200 plus seal Which you don't need£60, plus fluid say£30?.
So, I would say your quote is shite not very good tbh, as the whole auto trans, including selector switch, tc and new aft fluid could be replaced for less.
Imo, read and clear any engine and box codes. Drive the car as briefly as possible until symptoms return. Check the codes again, to see if the codes are recent and not historic. If you see a cam sensor code, which I think you did mention was present, change the cam sensor its fairly easy, fit the selector switch and try again, if symptoms persist source another box on here second hand and find a decent mech to fit it locally@50£ an hour ish.
That way you should have a complete working box for less than your quote, not JUST a new t converter with the same possibly buggered box re fitted.
All well trodden ground on here mate, have a google, it's all on here somewhere.