Although I should I have never really thought about live tournaments in bankroll terms. However being from Yorkshire I am unlikely to play in too many events that I can"t really afford as I have an in built spending control mechanism (ie: I am a nit).
It"s hard to say, over the years I"ve played £5 tournaments up to £2k tournaments and generally I would "flick it in" for any tournament up to around the £200 mark on my own money (without backing/sats) but I have been pretty lucky in that I started winning pretty much from day 1 so never really feel like I am behind.
For events I really want to play I would try and qualify online of the sats are worth playing (DTD springs to mind with GTE"s/overlay) but would never travel to play a live sat as it would then be a fait accompli that I would play the event anyway, having travelled there - plus I find live sats a pretty tedious way of sending my existence. I have also sold action in the past for events outside my bankroll that I really want to play but where I feel I can justify that I am worth backing at a fair price, usually to people I know quite well.
Live poker is more a social "treat" for me these days as I can"t play as often as I used to, so I tend to pick decent tournaments that won"t last more than 2/3 days but are "worth playing" and very much worth winning. So it is usually a mixture of social/backing/online sats, as long as the sats are value.