You've fundamentally over-estimated the potential cost of the materials required to make a wand.
In terms of the cores that Ollivander prefers, dragon heartstrings are likely to be relatively inexpensive if bought from the right (overseas) suppliers and unicorn hair and phoenix feathers can be picked up for free if one knows the correct locations. Similarly, the wood used is fairly mundane and can be obtained at no cost, merely requiring the collector to know what to look for, or by purchasing it from specialist providers.
Although dragon-breeding is outlawed in Britain, it seems to be pretty common overseas. Dragons themselves are not hard to breed (if one follows the appropriate instructions and has somewhere fireproof to keep them) and it seems likely that their heartstrings are simply a commodity item since they can be bred "for pleasure and profit".
‘Well, I’ve bin doin’ some readin’,’ said Hagrid, pulling a large book from under his pillow. ‘Got this outta the library – Dragon-Breeding for Pleasure and Profit – it’s a bit outta date, o’ course, but it’s all in here. Keep the egg in the fire, ’cause their mothers breathe on ’em, see, an’ when it hatches, feed it on a bucket o’ brandy mixed with chicken blood every half hour. An’ see here – how ter recognise diff’rent eggs – what I got there’s a Norwegian Ridgeback. They’re rare, them.’
Harry Potter and the Philosopher's Stone
Although unicorn hair is apparently quite expensive to purchase commercially, it's relatively easy to get hold of if you have ready access to a unicorn forest. It's likely that wand-makers would know this trick.
Hagrid’s face darkened and Harry knew why: Tom Riddle had contrived to have Hagrid thrown out of school, blamed for opening the Chamber of Secrets. Slughorn, however, did not seem to be listening; he was looking up at the ceiling, from which a number of brass pots hung, and also a long, silky skein of bright white hair.
‘That’s never unicorn hair, Hagrid?’
‘Oh, yeah,’ said Hagrid indifferently. ‘Gets pulled out of their tails, they catch it on branches an’ stuff in the Forest, yeh know …’
‘But my dear chap, do you know how much that’s worth?’
‘I use it fer bindin’ on bandages an’ stuff if a creature gets injured,’ said Hagrid, shrugging. ‘It’s dead useful … very strong, see.’
Harry Potter and the Half-Blood Prince
It's not really clear how many phoenixes there are in the wild, but they appear to shed their entire plumage at least once every month or two, meaning that any nesting area would be positively covered in feathers that can be harvested.
He wasn’t alone after all. Standing on a golden perch behind the door was a decrepit-looking bird which resembled a half-plucked turkey. Harry stared at it and the bird looked balefully back, making its gagging noise again. Harry thought it looked very ill. Its eyes were dull and, even as Harry watched, a couple more feathers fell out of its tail.
Harry Potter and the Chamber of Secrets
Similarly, the wood materials (oak, apple, ash, etc) are all pretty mundane, even if it takes a skilled eye to spot which are sufficiently magical to be used in wands.
Only a minority of trees can produce wand quality wood (just as a minority of humans can produce magic). It takes years of experience to tell which ones have the gift, although the job is made easier if Bowtruckles are found nesting in the leaves, as they never inhabit mundane trees.
Wand Woods by J.K. Rowling
It would appear that some wandmakers (possibly including Ollivander) also use wood sourced from farms that grow magically endowed wood.
Ollivander doesn't rely on commercial dealers. He appears to collect his own supplies (at basically no cost).
‘Ah, now, this is one of mine, isn’t it?’ said Mr Ollivander, with
much more enthusiasm, as Cedric handed over his wand. ‘Yes, I remember
it well. Containing a single hair from the tail of a particularly fine
male unicorn … must have been seventeen hands; nearly gored me with
his horn after I plucked his tail. Twelve and a quarter inches … ash …
pleasantly springy. It’s in fine condition … you treat it regularly?’
Harry Potter and the Goblet of Fire
He's also probably supplementing his income by selling any unused materials back into the general marketplace. His primary costs are likely to be the time needed to craft the wands, however much he pays himself plus wear and tear on his tools and equipment and the cost of running his shop, all of which could well be pretty marginal, especially if he's careful with his equipment and owns (and lives in) the shop.