1. Go to local Cobra events and look at cars and talk to owners. Take lots of pictures;
2. Decide on what is important to you, i.e. originality versus contemporary;
3. Decide how much work you want to undertake (some manufacturers sell cheaper kits, but you wind up spending just as much or more on surprises (like chasing bit parts and the # of hours to finish the body)
4. Narrow down the finalists, talk to the manufacturers at length (remembering that they are CAR salesman) and if possible, go visit your final choice before buying. Don't rule out buying used or partially finished kits. LOTS of good deals to be had there if you know what you are looking for;
5. Add at least $5k to your highest estimate;
6. Keep lots of cold, tasty beverages on hand.