DIY AC cable...which bulk cable?

I agree that the connectors make the difference in power cords.

I run direct 10 guage solid core romex from my breaker to the gear and found that the pricier Furutech gave better sound than the cheaper copper entry level IEC connectors.

I suggest you try the best connectors you can with some soild core #10 romex before you spend the big bucks.

Why $250.00?

You may like the $45.00 Furutech plug ends.
I did, that is until I tried the plugs further up the line, though they weren't quite $250 a piece,I did need two and so will you.
And for the extra money there was an improvemnt in the sound and the build of the better plugs is also much better, steel housing compared to thin plastic.

I have used 4 different wall sockets- hospital grade Hubbels which is a nice place to start for well under your budget.
Still under your limit is the Shunyata RZ1, and I felt it was a bit of an improvemnt, perhaps the cryo treatment?
I also have used the FIM blue/gold receptacle, and this was great when I had solid state gear as it seemed to take a bit of the edge off.
Now I use the Furutech GTX D gold receptacle and can't find a thing to fault with it.

It's solid constuction, has a solid connection and delivers a solid sound, it doesn't colour the sound as far as I can tell, it just seems to let more energy into the gear as silly as that sounds.At the same time it does seem to offer a little less background hash behind the music and there's more force and speed, more decay after the notes trail off than I've noticed with other recptacles that I've used.
I believe this is still in your budget,and one area where I wouldn't scrimp.

I have found that sourcing the wall receptacle and the ends of the power cord from the same company and in the same price category works better than splurging on the IEC's and scrimping on the wall receptacle.
If I had to decide which way to go, it would be to spend the most money on the wall plug.

Having said that,I would assume you will also be running dedicated lines?
If not, make that your priority, and scrimp on the connectors if you have to.
Your budget of $250 to $500.00 should include the cost of running dedicated lines, and then spend waht's left on the plugs.

I purchased the Furutech FI 48 R because they were 25% off.
I think they are one step below the top model.
They are a good match to the Furutech rhodium top level IEC in the amps,the only connectors in the line from the panel.
That line is simple 10 guage solid core Romex, and a generic 20 amp breaker.

I've had good luck with Furutech, but there are other brands that would offer similar improvements over stock power cords.

I have long runs so I use romex.
If the distance from the panel to the gear was short I would improve on the wiring,but I think better connectors can improve cheap wire, whereas cheap connectors will compromise the expensive wires.

I know that solder can have an effect on making a connection,so srew on or crimped is best,but isn't adding a crimped spade,adding something akin to solder?

Instead of a bare wire screwed to the connector,now you are introducing a third variable and disimilar metal to the mix.Maybe brass or tin?

I have thought that all the strands of copper may not make exactly the same connection to the connector.Hence, perhaps not a 100% perfect contact of all wires to the connector,and even some strands with minor cracks or breaks which could lead to a non uniform connection.
Just speculation,however,but it has come to mind.
That's why I like solid core wires.
But I might try flatening the ends so that more of the copper connects to the receptacles.
I believe some interconnetcs and speaker wires promote an oval type wire geometry as being a better conductor.
Although I have no experience with them to know for sure.

Instead of cheap dimestore spades,have you ever tried DIY and using silver or gold and fashioning your own type of spade?

That sounds interesting to me.
Perhaps the next tweak venture start up company?

Haven't tried spades yet, but I did improve the connection of the stranded copper wires from Furutech into Furutech power plugs.

Simply twisting the strands together using pliers(clockwise-counterclockwise,you decide)made for an almost solid core wire connection.

The wire is now firmly locked into the connector.

Probably not news to most folks here.