Hello, I would like to ask whats the cheapest way to fix all kind of scratches on the outside of the car (opel astra 1992)? Apprecihate all suggestions 
We need more information. How bad are the scratches? Is bare metal exposed? Is there any rust now? Do you want a perfect job or just some improvement?
Hello lion9car thanks for the reply. Well there are all kinds of scratches, some have exposed metal, some only surface, some just under the metal and there are few that already rusts. Also I would be happy with improvements already because its pretty old car and would just like to make it look better
Find A Reputable Auto Body/Collision Shop.
I managed one for a couple of years, once. I believe most good shops will have somebody step outside, look your car over and offer good, meaningful advice. We would have spent a few minutes with you, free of charge.
To have people on this site give you advice based on "Well there are all kinds of scratches, some have exposed metal, some only surface, some just under the metal and there are few that already rusts"is not going to be very beneficial. Without seeing each scratch and the over-all condition of the car, it’s impossible to help much.
CSA
Touch up paint makes the scratch look worse than it already is. It sticks out like a sore thumb.
Doing nothing promotes rust on bare metal.
A proper repair will cost a lot of money.
Sometimes the best thing to do is cover it with clear fingernail polish. It will seal the edges and covers bare metal.
A 1992 Opel Astra? The real repair would be way too expensive. Just “touch-up” the best you can and drive the car.
A thorough washing followed up by a wax job would improve the surface appearance. The wax tends to fill in the scratches, making them less apparent. Buy one of those easy to apply waxes and give it a go. If you want even more improvements, before waxing polish the surface with a polishing or rubbing compound product.
One word, MAACO.
Clean off the rust as best you can with a pick-type tool and maybe a little sandpaper folded to a sharp edge. Try not to make the scratch much bigger, work carefully. Brush primer on the bare metal. Lightly sand the primer back with a sanding block with 1000 grit sandpaper so it is flush with the existing paint. Touch up this scratch and lesser scratches with the correct color paint and a fine brush. Once dry, carefully wet sand the paint back with a sanding block so its even with the original paint. Finish with 1500 grit paper. Use rubbing compound to polish out the sanding scratches.Use finer polishing compound to smooth it further. Use a finer yet polish to finish it off and wax. It won’t be perfect but it will be better. Take your time and don’t sand through the surrounding paint and it should be good. Good Luck
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http://www.autogeek.net/