well look for these specs
1. i3 6100
2. the cheapest H110 motherboard you can find
3. the cheapest DDR4 1x8 GB ram kit you can find
4. a WD Blue 1TB HDD
5. a 4GB GTX 960 or R9 380, whichever one is cheaper in your country
6. a Zalman T-series mini case, or any case of your choosing
7. a high quality 550w PSU, use the tier list to help you choose
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html
for 100euros, I would buy used cards though. look for used HD 7950s and used GTX 660tis, 670s, maybe even 680s of you can afford them. though I mean getting some specs above should leave room for at a good GPU, more than 100 euros.