Thinking of visiting france at the beginning of July somewhere around the Vendee with a view to camping near to the coast. Just me and my sixteen year old son.

I have a regular vango airbeam tent that I could use but I think it may be a bit warm.

any advice on what type of tent to take for the conditions?

Cotton, polycotton, polyester etc etc I really have no idea what to use!

And the lower the price the better

Change clothes, not the tent - its easier and cheaper....

TBH, any tent in France in July is going to be warm. When we were at LeMans in June, our tent ranged from way too hot to bloody cold (and during one epic thunderstorm, exceedingly damp.....)

It can be very windy in the Vendee,so a strong waterproof tent is needed. Extra long ground pegs.

Hopefully you won't need to use its full potential,but it's a miserable holiday after a storm washout when camping.

If the weather is warm and sunny, any tent is going to be pretty uncomfortable from quite early in the morning; temperature and light will make sleeping late a bit of a challenge. Having said that, I love camping and spent most of 2 years living in a tent in various parts of France when I worked for Keycamp Holidays in my youth, including one summer in the Vendée.
Mosquitos will almost certainly be an issue (the Vendée is basically a giant swamp with a coast), so I recommend plug-in type anti-mozzie devices. You should be able to get battery ones or maybe take a big battery pack inverter-type thing (useful for charging phones, etc., too).
If you want a tip for saving money, try the Camping Municipal campsites. These are publicly run sites, but often very nice and a fraction of the cost of the "prestige" sites along the coast.
Bear in mind that many sites in the Vendée claim to be on the coast, but it can be a fair hike to the sea.

I'm off to the Ile de Re in July/August, with the other half, our then 11 month old, and my 11 and 12 year olds.

But doing it in a motorhome!