In terms of affordability Poland was and will be far cheaper than France for a similiar length of time. Of course it will depend where the games are played and if teams are based in one city in France. If not, the travelling costs shoot up. We had a 5 hour drive between Gdansk and Poznan which is easy enough once you have a couple of drivers. I spent ~€1500 for the ten days which included flights, campervan, diesel, food, drink and spending money. We ate out every night as eating in the camper van would have got too messy. If you were to do a similiar trip in France it would cost you far more. In fact, we spent about 2 and a half days in Germany as we flew in and out of Frankfurt and it was there that we spent most of our spending money....
Would definitely recommend it though. I'm almost 29 so it's unlikely I'll get the chance to do it properly again. Unbelievable experience.