The only reasonably priced good quality Pontiac crate engines I know of are built by Len Williams. And they're about $5000 & up, shipped.
400 Long Block
455 Long Block
The base brand new 350 sbc long block engine can still be bought for less than $2000 shipped, and has a 3 yr/100k mile warranty. So, there is absolutely no doubt that sbc is the cheap way to go.
Now there are cheaper Pontiac long blocks available. But they are sold by the large volume engine rebuilders, and will have the cheapest parts, like cast rebuilder pistons. Pontiac engine cores are also a problem with the big rebuilders. They most likely won't have the block/heads you want. The block they are likely to have will probably be the weak 500557 block. They do have some sort of warranty. But, if you need to use the warranty, you're out shipping both ways, and will get back the same quality engine you got the 1st time. But, I'm sure there are some out there, somewhere, who have actually got good service from one of these cheap Pontiac engines.
A quick search turned up this site. The best deal I see is a 455 for $2290 + $800 core charge + shipping. But, I doubt they even have a good 455 core in stock. They also show some 400 engines, for about the same price. But, those will probably have the horrible "8 eyebrow" cast rebuilder pistons. And it's likely that the only block they have will be a 500557. I could be wrong.
Here's one that's even cheaper. Description says it has a 7 yr/100k mile warranty & that performance options are avilable. Comes with #98
heads, which are low compression 2-barrel heads, with press-in studs. But, they show that 6X heads are available on 400 engines they sell. So, if you could get them to substitute the 6X heads, then that 455 MIGHT be a decent deal.
Here's one that's advertised as a Ram Air 3 engine. Nothing about it is RA3, except maybe the cast rods. probably has a 500557 block too.
Here's another cheap 400 listing. But, you'd likely not get the #96
heads, since a good ready-to-run set could easily cost $800-$1000.