I like potting soil that drains faster than my yard soil, and lets more air in. I should say "drains better than my AMENDED outdoor soil, because even my best soil in raised beds is 30-60% clay.
I consider pine bark mulch or nuggets "frugal enough" for a few 5 gallon buckets, and I mix in some % of "whatever" commercial peaty mix, or baled peat I'm willing to splurge for.
Lowes has very clean small bark nuggets for $4.20 per 2 cubic feet. I don't recommend Home Depot bark mulch because my local HD sells really dirty log-yard trash for $3.50 / 2 cubic feet. YMMV.
I screen the bark, to remove too-big nuggets and too-fine mulch fibers and powder. Big bark chunks make great mulch, or you can grind them smaller and re-screen them. Fine bark dust can be mixed into a raised bed just fine, just don't make it 25% bark all at once.
$ 4.20 for 2 cubic feet means 28 cents / gallon, or a 5-gallon bucket for $1.40. I think the bucket cost more than that.
If I want bark as an amendment to speed up drainage and aeration, like a substitute for coarse Perlite, I want bark nuggets or chips around 2.5 to 5 mm or 1/8" to 3/16". A little coarser than gritty.
If they are long bark chips or shreds (not spherical), I would like them up to 3/4" long and 2-3 mm in small dimensions.
If I want just water-retaining bark fibers and shreds, as a base for a soil-less mix, I start with the cleanest mulch I can find and afford, with as little dust and powder as possible. Then I try to screen OUT as much under 1-2 mm as I can, which is difficult.
This really fine stuff clogs up a mix and tends to exclude air the same way too much peat does. Instead of lots of really fine bark, you would probably be better off with a little peat or coir.
Right now the smallest screen I have is 1/4". Probably a 1/8" or 10 mesh screen would be better for working with mulch that includes fines and powder. Al uses some 1/16 window screening he found to "de-dust" the bark fines.
Anyway, to hold much water, you probably need a lot of the bark to be smaller than 3/32", 1/10", or 2.5 mm. Or instead, add a little peat or coir, or "whatever" commercial potting mix you have.
Of course, that's soil-less and nutrient-free, so you have to water with soluble fertilizer or start with bark plus compost and feed it things like fish fertilizer.
Others might prefer to consider the bark a "stretcher" and "aeration improver" instead of the base of the mix. Add 20% to 60% gritty or coarse bark, 1/16" to 3/16" (or even some 1/4") to whatever you were using, and knock your costs down by 15-40%. At 28 cents per gallon, it's cheaper than almost anything except what you can shovel from your own yard.
Big chunks like 1/4" or larger in effect reduce the volume of your pot, since roots can't penetrate it.
The finer the bark is, the less peaty mix you need. If your bark nuggets are mostly over 2 mm or 3/32", you need a fair amount of peaty mix or it won't hold much water, and you might have to water it more than once per day.
If you have a timer and a drip system and were thinking "hydroponics", I think fast-draining bark might be second only to expanded shale or clay nuggets. But I haven't tried that yet.
