Last gig I went to we paid £170 for two tickets. I'd happily pay up to £100 to see a band I am really into. Above that I'd have to seriously think about it.
Although a Barbra (note correct spelling, although she was Barbara until age 18) Streisand fan, I wouldn't pay anything like that to "hear her Fab voice" when I can do that anytime on my hi-fi (which cost less than £475 anyway). My ear is insufficiently sensitive to notice the difference, and my tinnitus wouldn't take a break anyway, so it would be money down the drain.
I could afford it but as much as I love Streisand I think it would be pushing it a bit. On top of that for me would be about £150 train fare, and about £170 for a reasonable hotel for the night.