Dr Craig harper's TSI mix:
50% Garlon 3A (Triclopyr Amine)
40% water
10% Imazapyr
It must be mixed in that order. The Imazapyr work on species that the Triclopyr is weak on and vice versa. Get you a good Eastwing or Fiskars hatchet and a spray bottle. One squirt per 3" diameter. I've done drill/fill using a cordless impact with a 3/8" auger bit and it works. But I've gone to using a hatchet for efficiency.

Triumph RTU is a generic for Tordon RTU and is available in quart bottles, the last I bought was around $20/qt. This may be a cheaper option if you don't have a large area to do.