To answer the original question:
50NL with a winrate of 2.5ptBB/100 long term and a volume of say 80 hands/hour would yield approximately $2/hour for each table.
However, setting volume goals are fine because you can control that outcome. Setting monetary goals in the short term is bad, because you can't control how the cards fall.
Poker is totally volatile. Some of the best high stakes players have logged 100K-150K break-even stretches and have beat the game for 2-3ptBB/100 over 1 million hands.
Top level SNG players have an ROI of 10% over 20K tournaments, yet can break-even for 1K tournaments.
All you have to do is take a careful look at sharkscope
It may appear to be a straight ascending line, but if you look closer you'll find looooooong stretches of SNGs where no money was made.
The same holds true for cash games. Different formats....but variance nontheless. Don't fool yourself into thinking (Oh well in cash games I just get it in good so it won't be as bad.) Then set over set, flushes and straights get beat by trips when board pairs, full house runs into quads, aces all-in preflop gets beat multiple times in a row, etc.
The players who succeed keep their head down, manage their BRs well, and never worry about outcomes. It takes a TON of patience. In fact, I think that is 75% of poker....a test of patience when you keep getting pummeled in the face.
Variance is a greater beast than most people realize until they hit it head on, which is why setting monetary goals is pointless.