Jeff
It really depends on the amount of money you are prepared to put for the car and also the kind of usage you may envisage.
Most importantly, it is necessary to understand how to register the car in France.
A normal approach would be usage for road and sometimes day track. Price for a middle to good car (ie GTD, Ford 302 engine, Renault gearbox, could be around 20 to 53 K Euro but price really depends on investments done on the car and if you buy in UK or Continent.
I believe the best price/quality you will find in the UK but registering in France may be difficult.There were some for sale in France but price is usually higher.
I suggest you ctc Frank Catt in UK (he is e member of the forum).He is always very help full for guys like you and me. In Belgium there is a classic car garage who regularly sells GT40s: Mecanicimport.com.
Good luck and keep us informed
Rgds
Fred