NN with Q-learning: which activation function with which cost function? • /r/MachineLearning

I've been messing around with Q-learning adapted with NN, after I read these two articles: I'm not yet ready to understand and implement conv NN so I just fooled around with normal NN. I've been told to use sigmoid as activation function and cross-entropy as cost function. The problem is it doesn't seem to work well with Q-learning since I want my output to be a real number, using a probability output seem like a bad hack to me. The papers I read seem to use the quadratic cost function but I have no detail about the activation function. I checked the github of someone who implemented all these and he seem to not use any activation function at all.