I have the DT770 80s and I used them without an amp for years and enjoyed them just fine. With that said I knew the whole time though that am amp would improve them. I recently just got an amp for them and they are much better now.
The amp I got was a Fiio E10. it has a DAC and amp and it does the job. It seems to power the DT770 fine and has made a definitely improvement. Here's the thing though, I did a bit more research on it and it seems quite low in the power department. Its enough to drive the 770s fine but I'm afraid when I move up to more power hungry headphones it wont have enough juice to drive them, so I'm a bit bottlenected. I couldn't pass up the deal I got on it though, they were on sale for 50 dollars US. At the 75 dollars US its back at now I would probably recommend something else.
I'm not that familiar with the other Fiio amps so I can let someone else come in that has more experience with them. I think you can get the new E7 for nearly the same price as the E10 and it has more power. If you do get an E7 makes sure its the new version, because its revised with a better amp and I believe it has more power them the old one, I think its the eo7k. The old one will have the same problem as the E10. There is the new E12, the E17 and the E9 that all have more power. The E12 and E17 have DACs too I believe. Pretty sure the E12 is under a hundred US here, but just. The E9 is just about a hundred US and the E17 is as well. Those prices are just for general reference because I don't know where you would be getting them or how much they may be in the Czech Republic.
What about Ebay? I know it can be a bit dicey sometime but if your careful things can be found there.
You could also try the FS section here, problem there is then your dealing with shipping from the US, most likely, or UK and I'm not sure how much shipping would be. If could possibly eat up any savings you would get but then again it could also provide you with more choices.
hmm those amps all seem to be above your budget at the link you provided in the other thread though http://www.heureka.cz/?h%5Bfraze%5D=fiio
Edited by loki993 - 1/28/13 at 7:49am