Not Cubs draft but lowest bonus in first 10 rounds was Padres 9th round pick Jesse Scholtens, RHP from Wright State U.
Scholtens got a $1,000 bonus.
Unfortunately, while at the formal signing, Scholtens' car was ticketed and towed for parking near a fire hydrant, so his net bonus is down to $610. However, Padres have agreed to provide a uniform, cleats, and cap at no charge to him.