Yes it works and I think the newer chemicals work faster. Not sure on costs but several guys on here will know.
Work's great! We sprayed 11 sections total and I think it ran about 15 to 16 thousand per section. Conoco sprayed a section next to my place and took out the cactus along my West fence line for about 100 yards inside the fence. It will knock the leaves of the mesquites but they bounce back, I'd do it after season when the leaves are off and everything is brown.