According to baseball-reference.com, there were 1,498 players drafted in 50 rounds in 2004. Only 202 of them ever played in the major leagues. That's a mere 0.00134%. Of that 202, 158 (more than 75%) were drafted in first 20 rounds. It makes you wonder why they bother drafting so many players. I guess there are 2 reasons: 1) once in awhile you'll miss a player like Mike Piazza; 2) you need players to fill up the minor league team rosters. As near as I can tell, all 1,498 players spent some time in the minors.
My Bottom 10 are the lowest drafted players who actually played in the majors.
Jeremy Horst. Pick #1,192 (40th round) by the Pirates. Horst was also drafted in 2007 in the 21st round by the Reds. I have none of his cards. The Phillies traded for him in 2012 and he pitched in a few games with the Phillies in 2012-2013. He's currently with the Lehigh Valley Iron Pigs, the Phillies AAA team.
Steve Edlefsen. Pick #1,235 (41st round) by the Red Sox. Edlefsen made some relief appearances for the Giants in 2011-2012. He became a free agent after the 2013 season and was signed by the Dodgers. He appeared in a few games for the Dodgers for their AAA team in Albuquerque but then retired in April. I have no cards of this guy.
2009 SP Authentic #153 Kyle Blanks
2010 Bowman Chrome Prospects #79 Eric Farris
2011 Bowman Chrome Prospects #116 Chris Schwinden
Chad Beck. Pick #1,285 (43rd round) by the Blue Jays. Beck was drafted again in 2006 in the 14th round by the Diamondbacks who traded him to the Blue Jays in 2008. He appeared in 18 non-memorable innings for the Jays in 2011-2012. He's currently playing in an independent league. I have no cards for him.
2011 Topps #536 Tony Sipp
2012 Topps Update #14 Jeremy Hefner
2011 Bowman Prospects Purple #10 Erik Davis
2008 Bowman Chrome Draft #14 Chris Davis
adderall -- for which he previous had a "therapeutic use exemption" but did not have for the 2014 season. I'd say Davis is far and away the best player in the "Bottom 10" but I'm always wary of a player with a drub suspension.