l have just bought a 2002 Peugeot 307 from an auction at the time when bidding l never noticed the rust on the drivers door, the rust is right along the bottom of the door, the paint has blistered! What is the cheapest way to make it look better? l have never seen rust like it on an 02 car.

you will have to get rid of the rust and respray the area. go to an auto parts shop and get some rust converter which reacts with the rust to stop it getting worse .if it is bad you may have to use body filler and buy a can of touch up paint. you can get D.I.Y sheets which should help

grind it off with a grinder first then treat it

Forget paint, grinders, rust treatments, etc.

Go for the quickest, easiest route. Find a door the same colour in a breakers yard. Many yards have a list of all the cars & colours on a computer, so u can start by phoning them, & they should tell u ''Yes, we have two blue ones'' or ''We have a silver & a red one''. They may not be able to tell u the EXACT shade of paint, & ur car may have been available in pale blue, medium & dark blue, for instance.
Unless they supply u with the key, u will need to get ur own door lock fitted, & of course, ur own cars' interior door trim. Make sure the glass is tinted the same shade! If u have green tints, & the door has brown or grey, u can have ur own glass moved over into the new one.
It can be very cost-effective to simply change the door, & could be a done-deal inside of an hour, rather than u putting the car in for paint.

The only real long term cure is a new door. Second hand is a good idea if you swap everything yourself. If you cant you will have to put out more money.

Agree with the door replacement, easier than treating.

Alos, and very importantly l would check for signs the car hasnt been in a flood, rust along the bottom and underneath the car can be a tell tale sign, check insude the boots and under the carpet for rust and/or silt.

new or second hand door, treating it will never get rid of it, it will come back sometime or another!