Cheaper than blinds: In the auto section of Wal-mart, you can buy “cut to size” auto window tint cling. It works very well, can be taken down & rolled up when you want to let in more light and takes up no space, so whatever window coverings you use will still look nice.

You will need to have something that has some insulative quality to it. Mini blinds just don’t cut it and I’m not sure you will find window treatment cheap.
Here’s what I have done and it’s only temporary. I had some R-13 wall insulation and inserted 2 cut pieces into a 39 gallon hefty bag. I used whatever masking tape I had and taped the batts inside the bag to keep them from just sliding down to the bottom of the plastic bag. And then I used push pins to fasten the whole thing inside the window opening. It blocks out the light as a solid wall will.
I live in the same area of the country and with this intense heat it’s just going to be hot.

In addition to the above suggestions, how about turning up your thermostat to 80º during the day and 75º at night?

Those are the settings that I use and I find them to be very comfortable, but then I’m a minimalist when it comes to hot-weather attire.

In my experience with extremely hot weather it really doesn’t matter when you move the thermostat up so the house is warmer in the day. When you come home and turn it down to cool more , the unit is just going to struggle to drop the temp. Even set at 80, if it’s 110 outside, the unit is probably not even going to shut off, and if it does it will be for a few minutes at best but it’s still going to be constant running. It’s like going downhill faster than you need so you will have momentum to go back up the next hill. So let the house get really cold in the morning and don’t open the doors any more than is needed. Hopefully it will carry further into the day before it starts getting uncomfortable.
Block out all the windows you can and try to not use the oven.

I got my blinds from here

Custom sized blinds for 8 windows was under $300 including shipping. They had to redo a couple of the blinds because I measured wrong and didn’t charge me for fixing my error.

You could use some of the “blackout curtains” from Wal-Mart or Target. These come in many colors, but the side facing the window is white. They’re heavy enough that if you put them flush against the window frame (not the window) they create an insulating layer and help reduce the temperature in the house several degrees. The flip side is, they do block out any sun, so if you want sun, I’d go with @SpatzieLover‘s suggestion.

I noticed black out curtains suggested by @linguaphile, I was going to say the same, but suggesting Bed Bath and Beyond, they are amazing. Very reasonable price, and really block the sun.

Pre-cut faux wood blinds at Home Depot would be my suggestion for blinds, they close perfectly flat, they can cut them to almost any width, and you adjust the length yourself. They look great also. They come in white if you don’t want a wood finish.