I don't buy a bunch of ammo at a time, either, so I have found Wal-Mart and Academy to be my favorite places to buy locally. Internet prices are great...until you add in shipping, which gets spread out only if you buy quantity. In other words, buying a box of ammo online to save $2 price will probably cost you $5 more than at Wal-Mart, just because of shipping.
That said, for .38s, I'll get the Winchester USA valu-pak. Its adequate for range time. I found some remanufactured stuff at another local store that was about $9 or $10 for 50 rounds. I haven't shot these yet. They're semi-wadcutter (lead) - again, good for targets.
For ..357 practice, I like Blazer's aluminum cased 158 grain stuff. They are HPs, but they are priced very competatively. They're a medium load - not smoking hot, but not powder puff either. I would highly recommend these if you're learning to shoot magnum loads. Price wise, they're around $15 at Academy and Walmart. Academy also has their own brand, "Monarch" that's a bit hotter - no chonograph data to back that up, just "feel" - and right in that price bracket.
At this point, I would also strongly urge you to not spend hard earned money on the high-dollar stuff...the $18/20 round stuff. That's defensive ammo and great stuff, but to just pour downrange...no.
Buy what you can afford, to make your trip worthwhile. NOTHING worse than getting there, having a ball, only to realize you just punched your last hole in paper and you want to go another hour or so.
I try to pic up a box of SOMETHING each time I hit Walmart: .38s, .357s, .45, 9s, or a half-dozen boxes of .22. It spreads out the purchase "pain," but makes a range session worth the trip.
For what it's worth, from one $ consciencous shooter to another...
Quoheleth