It really depend on the player in question. It's not uncommon to see guys drafted in the 8th round or later getting $750,000 - $1,000,000 signing bonus, which is late 1st round/sandwich round/early second round type money.
There is no hard number, just a number MLB recommends. As for what MLB's slot recommendations, the best I could find is this
, which shows the average signing bonus the past few years for the 11th, 57th, 89th, 123th and 153th overall picks (which are the Rangers' first five picks this year).