Can we fly them over the country as transport?

There were some business people who flew old F-86 Sabre jets as private planes. Just be aware that upkeep on a fighter type plane is very, very expensive and they drink fuel like crazy. Eventually the people who owned Sabres got rid of them as the upkeep and fuel cost was stupid high. And Russian planes are even thirstier and getting spare parts is a nightmare.

No, they cannot be used for that purpose because they can only be certified for civilian use in the Restricted Category. One of the few ways they're allowed to fly is for scientific research purposes or under special "flight display" authorization, i.e. at airshows and in practice / training for airshows, or for transiting to or from such events. Besides that, they would be absurdly expensive to operate and maintain compared to modern executive aircraft and they couldn't operate from most airports due to noise restrictions.

Sure, if you have the money to burn, but they are not practical transportation. It would be a bit like using a 1929 Duesenberg as your daily driver,.

They require a huge amount of maintenance, parts are rare, burn an incredible amount of fuel, are not very reliable, have limited range, no space to carry anything other than the pilot, and are very uncomfortable, and would be impossible to buy insurance for if being used in that manner.

It also requires a great deal of specialized flight training - a turbojet normally requires a type rating, a rating for each specific type of aircraft. Since an old fighter does not have a type certificate, there is no type rating. You have to go through the process of requesting and being approved for in individual "letter of authorization" (LOA), and unless you have previous military flight experience, you would have to jump through a lot of costly hoops to get approved for one.

There are old Soviet fighters under private ownership, but they are mainly only flown to airshows, and for brief flights to stay current. When they come up for sale, they are surprisingly cheap - the MiG 21 below is 1/3 of the price of a new Cessna 182 - but that's because they are so costly to fly that the market for them is tiny. You could spend 3 times the purchase price on yearly operating costs.

http://warbirdsnews.com/warbirds-news/airplane-mig...

That depends in which country you live in, and you epically failed to mention that. Oh, and aircraft is singular and plural, no s needed.

They are not currently certified by the FAA so no. And if they are, you will have to find mechanics who are certified to work on them. Good luck on that one.