Jonboy, im quoting new for the rolling road time yes as I dont know anywhere that does it secondhand for carb setups and mapping ignition
Bottom line is you are looking at about a grand to do it properly on carbs secondhand, and about 1500 on TB's, and you are looking at about 1500 new on carbs and 2000 on TB's
And thats if you go for "branded" TB's if you are prepared to get a bit inventive with a bike set and cheap management, you can bring it in for the same or less than you can with carbs.
Your resale value on the 1500 quid TB setup 2 years later is 1500 quid, thats the best thing about it on a standard XE, no mapping costs needed, and no depreciation.
So cost of ownership over a 2 year period = zero IMHO