Basic 12g copper speaker cables to $$$ cables.

OP it has NEVER been about dollar amount. It is about the construct used and how they were put together. There is NO SUPER duper change because of price.. There is however a correlation between a good business model that gives you more each time you pay more.

Me I jump to the position I like in sound, and have for quite some time. Speaker and gear type, really don’t change for me.. Just like the rooms I use.. The cables I build would be tough to better for what they do.. I don’t care who makes the cables... I have had some serious cables over here for 2 to three weeks at a time to be fair off and on for 4-5 years now.. It is tough to beat some of the weaves, and helical builds, with just a little effort and a few good parts.. YES some are pretty spendy. ALL under 500.00 usd, No matter what I do.. Pure silver $$$$

I’ve built cables for 45 years for HEAVY equipment.. this stuff is pretty easy to figure out.. It’s A Cable for God sakes.. Not made by cable gods.. just stiffs like me... with good parts.. I’m a happy fellow..

If was gonna spend money on cables, I use the business model I posted. The more you pay the more you get...That is what most of us want anyway.. RIGHT?

Regards..

So here’s what I have. Maybe someone could offer specific low, mid, and high budget good matches. I know even less about interconnect cables, so I’m open to hearing about the difference they can make and what someone might recommend as well. I have a musical fidelity a308 amp going into ATCSCM 40 V2s. It’s a very complex, difficult room, with no options to change that part of the equation.Any ideas?

I’ve been all the over the spectrum with cables, including a $14,000 loom of Nordost Frey 2 with the QX4 and QB8 etc. In my opinion cables are the last 10 percent that can really increase your connection to the music. They don’t need to cost as much as a car, but if someone tells you they don’t matter, get advise elsewhere.
The first indication of a cable change for me comes from background listening over the day. Little things that get your attention, or not. Give them time don’t just cycle through them like socks.
I’d say $8k system, start with $1k if you can. If you can get a set priced right you might be out $50 if you resell. Maybe you are satisfied maybe not, but that's what I would suggest.  More money doesn't always mean better, but it typically does IMO.

Find a store, any store, that has speaker cables, power cords, or interconnects they will let you either demo in store or take home and try. Does not really matter at this point if you listen to speaker cables, interconnects, or power cords. They all make a difference. The question you are trying to answer, how much for YOU to hear a difference. Only you can answer this question, and you can only answer by trying. 

Me personally, a very long time ago, I did this and the difference between my freebie wire and the one the store had was night and day, and that was "only" a $175 interconnect. But- and this is a very important BUT!- you may not hear any difference at all. Or it may be that in your system a cable upgrade is not appropriate anyway. Like if your speaker cables have to go 20 feet, one is ten, must hide behind furniture, etc. In that case you will be smarter to go with interconnects and power cords that will give you the same improvement, but without the hassle and expense of speaker cables.

First though you must answer your question by actually going and listening and finding out for yourself.