How much is each chip price
Not sure if T17 uses BM1396AB or another chip, but the price should be in the 5-10$ range per chip, but that isn't the issue, the issue is how are you going to replace the chip? you will need a professional to do it, another potential problem is it's unlikely to get 1 chip order, you might need to get a whole strip of 10 chips, plus shipping and all of that, it makes fixing the hash board expensive enough to just forget about it, but of course, do your own math.
T17 40th goes for about $370 in china (used), so my guess that a used hash board would be 20-25% of that? so $70-90 is my guess.
i see some videos that one faulty chip on a hash board could cause problem...
Yes the way these boards are made, 1 bad chip stops 29 other chips.