Hey Sebas ,
There are a lot of tablets actually for sale under 300 $ , could you please give us what applications you want to run & how large you want the screen to be ?
I can't really recommend a specific model , but try to stay away from low-end samsung models at all costs .
You can start searching here :
Amhaz ( Store already has a sticky post ) :
https://www.facebook.com/AmhazOriginal/
Pcandparts.com ( Link to the notebook section , scroll down for tablets ) :
http://pcandparts.com/notebook.htm