Whereever I go to answer newbie questions which have been asked many many many times before Edwood was already there.
However, if sound quality is your greatest concern and in respect to your budget I'd recommend a better soundcard, but this is obviously no portable solution at all.
I think the Porta Corda III USB from head-fi sponsor Meier-Audio matches most of your requirements(external, computer connectivity, headamp capabilities, portability, budget) except the optical in.It's lightweight and battery operated and therefor totally portable, and powering it by a stationary power supply at home is an option.
Jan Meier is located in Germany which means no hassles with customs.It costs 230 Euro shipping included, and
here is the english speaking website.
Look for Products --> Amplifiers.
BTW, at least the european members are aware of where Estonia is located, you are part of the EU.