"low priced" doesn't go well with the idea of "suitable for bonsai."
My recommendation: Jim Smith's nursery in Vero Beach Florida. http://www.jimsmithbonsai.com
His prices aren't out of sight, and he grows plants JUST for bonsai.
I agree that "low priced" doesn't go well with "suitable for bonsai". However, pre-bonsai ficus and schefflera, of the species I mentioned, should not cost more than $10-$20 per potted cutting and no more than $20-$40 for an unstyled tree in a quart pot. Once it's in a pot and someone made a single cut or put on a single wire, well, then, the sky's the limit. Mass-produced trees hit $30-$40 right away and pass $100 after two years in a pot. Since the initial poster is looking to get started with ficus and asked for bonsai stock or pre-bonsai, I'd recommend nothing more than $10-$20 for bonsai stock and $20-$40 for pre-bonsai.
Bear in mind, I'm from New Orleans where these trees can be defoliated in March and again in August with no stress to the tree. Here, the cuttings root nearly 100% of the time. Keep them moist and aerial roots drop like crazy. They're so easy to grow that members snatch up cuttings at our meetings, and get hold of cheap starter trees at our annual auction. I donated a dozen schefflera aboracola and ficus microcarpa year-old cuttings to the auction and we priced them at $5 each. Next year I'll have a slew of Green Island ficus cuttings going for pretty much the same price.
Cheap stock and cuttings CAN make good bonsai if you pick the right source.
jimsmithbonsai.com has only 18 out of 152 trees for sale. Here they are:
Cape Honeysuckle: $1500
Crepe Myrtle: $500
Ficus Green Island: $800
Ficus Green Island (2): $1500
Ficus Salicifolia : $3000
Ficus Salicifolia : $2000
Ficus Salicifolia : $1900
Ficus Salicifolia : $1800
Ficus Salicifolia (4): $1500
Ficus Salicifolia (1): $1200
Ficus Salicifolia (2): $800
Ficus Microcarpa: $2000
Ficus Exotica: $800
These are beautiful trees! Since they sold 88% of their stock at these prices, I have to say they are priced exactly right. These are not mass-produced trees. These are specimen trees. However, these are not learning trees.
I searched eBay and found a site with trees you may like: wigertsbonsai.com
They have pre-bonsai for $25-$40, which is quite reasonable from what I'm seeing of their photos. They also have specimen trees for sale at prices that make jimsmithbonsai.com look like a bargain basement sale. There are some acacia which are catching my eye. I just may shop there myself.
Here's a tip on growing aerial roots: Place all of your stock material close together under a sprinkler and go on vacation for 2-weeks. Then come home and put off the chore of putting them all back up on your benches. I seem to do this every Summer and when I pull the trees away from each other, I've got fresh aerial roots coming down like crazy. The denseness of packing them in tight means that the humidity levels are higher than if they were up on a bench. No, don't do this with other trees. The higher humidity also leads to fungal problems.