How large is your aquarium? IMO, co2 booster or excel wouldn't necessarily break the bank in a nano tank or two. But in larger tanks or if you have a lot of small tanks, Metricide 14 is very cost effective. It's approx 2X stronger than excel so you can either dose a little less or pre-dilute it to excel strength and dose as you would excel/CO2 booster.
If you get Metricide, there's an activator bottle that you DO NOT USE. Just disregard.
One more thing. I haven't searched for a while, because you get a lot of Glut for the money, but the first time I bought Metricide 14 is was approx. $20 a gallon shipped. Last time I needed to replenish my Glut I couldn't find that price again. Metricide 14 jumped in price. However, I did find an eBay seller that was selling Omnicide 14 with a picture of the Metricide bottle with a description of "Metricide / Omnicide" in the title. Anyways, after a little research, due to my apprehension, I felt confident enough to get Omnicide this time around because it was approx. $20+ shipped for a gallon. I've been using it for several months now to no ill effect. Just thought I'd share that in case you wanna save money.
Here's a calculator if you want to dilute the Glut precisely. Otherwise a 50/50 is sufficient.
http://rota.la/glut/