How is the life of a professional GM with ELO around 2500? How is the life of a professional chessplayer with ELO around 2500? I mean, someone who is no doubt strong, but hardly a top GM? How does he make a living these days, if he hasn't another job?
I know a few GMs in 2500-2600 range who would be considered professional -> ie chess provides the primary means of earning income for them.

It is very hard work with wages not matching the effort/skill spent:


Being the primary player for medium club team (European/Middle East/Far East)
Teaching (preferably within said club as it guarantees steady supply of clients) 
Being an personal assistant/coach to another player 
Playing for hire for a stronger club in say Bundesliga lower boards
Actually getting some prize money in medium sized tournaments 
Books provide a tiny bit of income, but mostly are used for name/brand building for the next item
Selling training coarses - again only a few can make a living from this
A growing but still insufficient means of income is streaming, a few personalities can pull it off
Playing in special norm tournaments, in Eastern Europe GMs get about 250-350Euros for a week long tournament, where IMs/FMs/untitled have to pay 100-300 Euros to compete for GM norms.


That said most GMs around 2500 have other means of living besides chess.