That's a bit of a strange bike, the frame is a dated design, very similar to what you see on BSO's but there are some good parts on it, from the photo, the forks and brakes.

Woudn't look at putting too much into it, you mention brakes, you would also need new wheels, and with the other part mentioned, you would be better looking for a more modern bike, with these parts already spec'd, and breaking and selling the good parts from the BH.

As you are listing your prices in Euros, but don't give a location, would look at Decathlon, and a bike from the Rockrider range (plenty of options) as these are available through out Europe to compare to what you can get with your given budget.

For the 'shifter bolts', these should be easy to source via a good LBS, either they may have them in a spares box, of get the part number from SHIMANO Dealer's Manual / User's Manual you will need to find the model, then the Y number, getting the old plastic out will be difficult, but possible.