Alternatively an LAA type two seater especially group owned is much less expensive - if slower at 95 mph than your 100kt 172.
Free landings a many French airfields help too. For a long trip, time in the air and stage length is less pressing, but admittedly not space usually for loads of luggage.
I'm hoping to make it to Blois by 80 hp Rans for their annual big 'ULM' exhibition this w/end complete with my tent and basic camping gear.. Stopping for Customs at Abbeville en route. Then after the w/end continuing further down into France.
Hourly cost is "optically£ fuel only, say £20 per hour as ownership overheads are there whether flown or not !
mike hallam.