If you have a Cabela's near you, and can get one of their credit cards, there are good prices on 158gr .38spl and .357mag. Credit card holders sometimes get 20 percent discount codes that can be stacked with sale prices.

Here is their current sale price on Herters ammo, and you could possibly discount that another 20 percent with a code. I order online for in-store pickup so that I get the quantity I want. I've been getting all my revolver plinking ammo this way for a couple of years now. They seem to run these sales every couple of months.