Not an expert, but have done a fair amount of reading on it.
Garden Lime is around 34% Cal, and 3.8 Mag (it may vary a bit between brands). 40 lb. bag is less than $4.
Dolomite Lime is the stuff most MJ growers use when making soil/less mixes and is around 20% Cal, and 10 Mag.
I saw one smart guy who mixed the two types of Lime around 50/50 to achieve what he said was good ratio split of Ca:Mg for herb (it's 54:14, but forget what he said good target was).
Of course stay away from the hydrated stuff. Generally folks suggest 2 tsp Dolomite per gallon of soil/less volume as enuf for a whole grow.