Face and chase should be in the $20-$30 range. If it isn't then buy the tools yourself, learn how to use them and then face and chase 10 of your friend's bikes for $20-$30 and make back your investment.

Should it be done? Yes.
Just for new installations? No.
Does it "have" to be done? Mostly not.
Can it be done more than once? Yes, but pay attention to your overall BB shell width...most BB's have a minimum acceptable BB shell width.
Does it need to be done for older self-contained systems, or just the new external bearing type BBs? Both, although I have seen sealed BBs work just fine in shells that were so bad that when swapped to external bearing type BB and crank the spindles bound solid and couldn't complete a revolution.
Can it be done with a file (the facing)? Yes. I've done it that way before. Then again I used to be a locksmith and have hand cut keys with a file before....Get some Dykum and pay attention to what you're doing.