Guys do you know any cheap cases which come with good sound properties? I know already a lot of 'silent' cases but all are in a price range too high. I'm looking at the real cheap cases like Cooler Master 310, some Gigabyte cases and MS-Tech cases. Also a Antec Three Hundred second hand, but because of the thin material and open design this one doesn't have that good sound properties to begin with. I hope you guys have some advice, thanks in advance.

System:
AMD X3 455 with onboard graphics. So no high-end graphics cards in there.

I'm not sure of anything decent in that price range. Maybe look for a second hand Antec Solo (the original version), Antec Sonata 2 or Sonata 3? Or even an Antec P180/P182. They seem to sell pretty cheap second hand nowadays.

Take a look at http://geizhals.de/471340 Aerocool QS-200. If you set the fans to 7V it should be kind of quiet, if not enough you should swap the fans. The HDD mounting isn't as prone to vibration as in standard cheapo cases.

At this price range people tend to take some joe case that isn't too open and cover up any vent that's not needed, then stuff spare areas with foam if necessary. Thin material isn't much of a problem as long as it's steel, just add some weight to the surfaces with vinyl tiles or car shop bitumen sheets. If looks isn't too important, adding weight on the outside is real simple of course. For this build a half decent CPU cooler will go a long way and then it's up how the the harddrives can be mounted and whether they are very noisy or not. This system won't need much in the way of speedy case fans, perhaps the powersupply will be the noisier fan. A case with the power in the bottom is generally preferable.

I had Antec 300 by itself it wasn't quiet, but it was cheap and after work: cutting fan grilles and replace some of them with wire grilles, adding two layers of bitumen matt floors, top and sides + foam on bottom and sides, I quadrupled its weight and it became very quiet case with Nexus Fans. That means if you can get bitumen matt cheaply (local car parts and such shops should have more than enough choices of them) and have tools cut off fan grilles ( I used regular cutters and elbow grease) and bit can-do attitude you can make almost any budget case very, very quiet and even silent ones so much that getting that extra 20% sound off needs more work than anything else, like suspending hard drives, swapping graphics card cooler and such.

Worst quality of 300 in my sample was 140mm tri-cool fan on top, fine and quiet fan, except when put vertically like on top, it racket entire case since blades were slightly off balance. It made a penny I put on top of case dance and bounce. Why I started modding and adding bitumen matt.

Cooler Master Silencio 450/550/650

+1

If you're strapped for cash and not in any hurry check out eBay.
I bought several cases from ebay and except for one I was completely happy, but that one wasn't expensive so I'm not unhappy about this one.
If you don't need the latest or most popular case, you can get great deals.
Look for Antec P150/Solo ..., Chieftec (Dragon) look for newer models that can hold 120mm fans, Lancool or older model Lian Li PC60,etc. (construction quality was better, but the hard drive mounts have no decoupling and are made from aluminum means they might rattle.).
Don't buy MS-Tech, you can bend these cases if you look at them the wrong way.

Thanks guys for your input. I'm starting to think I just need to spend 10 euro's extra to buy for example the Nexus Thrio 310 Silent Case or BitFenix Outlaw. Too bad some cases have glow fans but you can't turn it off so these cases are no option like the Sharkoon Ms120. I'm not that much of a DIY guy and most of the materials are not cheap here either.

You can. Just cut the apropriate wire(s) leading to the leds.

Turned off for good.

What storage? Just a SSD, some 7200rpm HDDs or something in between?
Bitfenix Outlaw looks like a great case.