What video game system do you recommend I start my console game programming on? I'm looking for a programmable video game system + manual on eBay or Amazon. Can anyone help me out?

I'm O.k. with old-school. It matches the type of game(s) that I'm trying to create.   

I really enjoyed the homebrew work I did on the PSP; it was easy to get set up for and reasonably well-documented. If you want something older, the GBA is also a fun platform.

What are the recommended environments for both of those? I'm currently using Unity. I hope that'll do. Will it?

Cygwin, I see.

Do I have to buy a programmable GBA?

Unity will not deploy to either of those, so it's not an option. You will generally want a physical console to do this kind of stuff on, yes, but it usually doesn't need to be anything special. You will generally perform some kind of modification to the console to enable it to run homebrew software. If you want you can usually use emulators as well.

If your goal is not actual homebrew low-level development on these platforms... if you want to use Unity instead, that matters. Your platform options will be limited to the current major consoles supported by Unity (check their site) and you'll have to be an official registered developer for whichever of those consoles you want. Obtaining this may cost money and may involve applying for the license.

 Thank you for responding so thoroughly.

I'd like to start programming on a GBA. Where should I go? And will just getting a flash cart do?

It is one piece, but not the whole thing.

Most of the GBA homebrew died off a decade ago when smartphones proliferated and the GBA ceased manufacturing. Sites like GBADev.org used to be one of the go-to sites although I haven't followed them for a decade or so. 

If you go that route you will have a small and shrinking group of enthusiasts to help with issues, and unless things have changed dramatically the most common approach is to tell you to look at the raw assembly and figure things out on your own.  The entire development chain is unsupported, individuals figuring out from memory during their time working on the systems, from assembly dumps, and from the occasional illegal leaks that were cleaned up, individuals were expected to figure out on their own how to do everything.

If you're looking at putting something out for showing off, programming for your cell phone is probably going to be easier and include enormous support groups.

If you want to develop for GBA, you'll need at least an emulator (if legal in your location) and probably want a GBA and at least one programmable cartridge (if legal in your location).

Then you'll need to find the right libraries and compilers that target the platform. GbaDev can help with links to those, although they're likely suffering from link rot.

If you want to debug, you'll need to follow tutorials that either connect to an emulator for debugging, or try to find whatever you can to debug on the device. 

It is not an easy path, but if you particularly enjoy the device and want to invest the effort --- which will include learning to at least read assembly code --- it may bring some emotional rewards to you.

    I see. My deal is that I want to develop for a console and I want to do it cheap/free. Do you have any other suggestions besides the GBA? I don't really want to develop for cell phones. I'm down to develop for stone age systems. The more ancient, the better.

   The GBA seems like an acceptable package. Could I get a complete list of hardware/software plus accessories needed to develop GBA games? Like a GBA and a disk writer and a development environment are all I can think of.

"

int main()
{
	char x,y;  
	unsigned short* Screen = (unsigned short*)0x6000000; 
	*(unsigned long*)0x4000000 = 0x403; // mode3, bg2 on 

	// clear screen, and draw a blue back ground
	for(x = 0; x<240;x++)   //loop through all x
	{
		for(y = 0; y<160; y++)  //loop through all y
		{
			Screen[x+y*240] = RGB16(0,0,31);  
		}
	}

	// draw a white HI on the background
	for(x = 20; x<=60; x+=15)
		for(y = 30; y<50; y++)  
			Screen[x+y*240] = RGB16(31,31,31);  
	for (x = 20; x < 35; x++)
		Screen[x+40*240] = RGB16(31,31,31);  

	while(1){}	//loop forever
}

"- I love that. It really resembles how I used to code. 

A Flash cartridge and a GBA are all you recommend, right?