If you've got plants, shrimp, fish and such... I suggest trying to sell a few in order to pick up a gram scale. The etra $5-$6 it costs will save you hundreds of bucks down the road. You won't regret it, as it will come in really handy in this hobby if you can swing it.
I've been using the same $7 jar of Safe for a couple years. Probably would have been through five or six gallons of Prime in that amount of time.