I do not know the cost of repairs - but did you try what I have mentioned just above your post? You may need to connect to the device to a charger if it doesn't work at first as battery would be necessary to enter the mode that I described.
Edit - it wouldn't respond to a PC - regardless of its condition - if it were off (nor would it display anything when connecting a charger w/ a corrupt installation)... It would only respond to the buttons being pressed in the way that I have mentioned. And sometimes you have to press and hold power+volume up to force a restart first before trying the power+volume down another few times. That is the only way to really see if your phone is bricked. I have read through countless posts on this forum where people RMA'd their not even bricked phones.