Welcome Mohammed,
I agree with ripinator be patient, and ask these guys here what to look for as far as rust trouble spots on these cars. Typically cabin floor and trunk floor rust is common on any old car, but if you dont know how to weld to fix it can be costly.
Take a magnet with you when you go looking, especially at a repainted car. If theres body filler it wont stick. Lower fender edges, lower edges of rear quarter panels, bottoms of doors are typical rust spots too.
Also a lot of parts on these cars are not reproduced and original parts in good shape can be hard to find and costly. For this reason look for the best condition vehicle with the least amount of defects in the body panels, interior, and trim that you can find. This stuff can be hard to find in good condition if it has to be replaced. Mechanical parts are easy to find and not a deal breaker as its easier to fix mechanical stuff than do body and paint. Lots of parts are available for these cars at Rockauto online.
I am looking for a good 70 newport hardtop 2 door, or 70 fury hardtop 2 door. I am looking thru ebay, craigslist, and other sources. Hemmings motor news can be a good source too. I am being patient. I will know when the right car pops up. I am wanting a turn key driver that i can fix minor issues as i drive it. I have a long term restoration project, so i dont want another car completely apart lol.
Good luck on your search, and happy hunting.
Matt