Apple lowered the entry price of an iOS phone to $400 this year. There’s more profit to be made via monthly payments for services, so getting more iOS and macOS products into people’s hands is in their interest.
I’m not saying they will sell third rate quality products like $400 laptops or $200 phones and tablets, but they are interested in lower prices and making up for it by getting people to purchase more from the whole ecosystem.
Apple has lowered the prices on all of their major product lines: iPhone SE ($400), iPad ($329), Apple Watch ($279).
I can't see anything in the way of Apple creating a lower priced MacBook SE at around, say, $700. With that move, Apple could essentially own the technology stack (iPhone, iPad, Mac, accessories, etc...) of millions of consumers previously priced out of the Apple ecosystem, consequently driving services revenue.
It would be interesting to know how companies like Apple account for the market of older models and how that feeds into their services revenue. For example if you can go on Woot and purchase an iPhone 8 for $399, while Apple didn't make money off of that sale, they will certainly make money from app purchases and iCloud subscriptions. And at $399 there's bound to be people willing to purchase an iPhone even if it's older. With Apple's iOS support reaching back several generations, it's not always a bad deal.
So in a way, even though Apple isn't making money directly off the sale of that old iPhone, they're still able to feed this lower-end market and make money from apps and services, without directly lowering their prices and maintaining their perceived high-end status.
Edit: I gave an iPhone example but it certainly extends to the Mac lineup as well.
I made up the numbers as an example. It doesn't really matter, my point is that Apple's old devices, be it iPhone or Mac, still have value years later. So even when people are fishing the old stuff from the bargain bin sites, Apple is still making money off of them. As a result, Apple doesn't need to compete with the $400 Dell because people will still be buying the 5-year-old MacBook Air from the bargain site and with it, buying app/iCloud subscriptions.
I’m not saying they will sell third rate quality products like $400 laptops or $200 phones and tablets, but they are interested in lower prices and making up for it by getting people to purchase more from the whole ecosystem.