Affordable vs. ultra expensive speakers - what's the difference?

That depends upon you and where you are in your audiophile journey.  $50,000 speakers are an endpoint you build your system around think long term investment.

3k speakers could be an endpoint if you are satisfied with the sound but will be a limiting factor in the future if start improving the supporting equipment and will probably be replaced, maybe several times with the possibility of spending much more than the $50,000 depending on where you end up.

The difference is the importance of sound /  music to you now and in the future.

I still miss the robot references.

This is a very silly question. Listen to them and let your ears be the judge.

For the $ for a Ferrari...which are really nice....'cop bait', though....

I can buy a modest house.

Plus a Lotus. (Most cops don't know what they are.....👍)

And a nice Yamaha sport bike. (If I'd want to draw attention from the PD...)

Currently I DIY my speakers....not the 'box', the driver itself.

As is said: Priceless.

At least, to my ears and my predilections....;)

Pick your path....

Precision costs more money, but does not always guarantee better performance. Exotic materials cost more money, but do not guarantee better performance. There are also costs associated with R&D that are defrayed over the total expected run of a product. A lot of high dollar items sell fewer units, but have a lot more R&D costs. The scrap costs may also be higher because the finish standards are more stringent and the materials scrapped cast more. Not everything that makes that product more expensive may be important to you, but you’ll still have to pay for it as part of the package. You can arrive at any conclusion of relative worth simply by weighting the selection criteria a certain way. As a value proposition the more expensive item is rarely preferable. This falls in with diminishing returns. However, sometimes the performance aspired to is not a logistical problem that can be optimized economically, but a conceptual problem instead. “Can this be done?” rather than “What’s the most efficient method to reach a specific result?” Most of our systems are well within the realm of logistics and compromises or trade offs based on economics. But those systems unconstrained by conventional limitations are fascinating to read about.  

Whats affordable for you may be cheapy stuff for someone who earns allot more. whats affordable for that guy maybe too expensive for you.

Regards, I would still say focus on a Good Room first as this will make allot of the diffrence.