Here's my solution for a very low cost and period correct car stereo. It's a 3D printed faux radio that I designed a while back. It looks nearly identical to the real thing and it's now functional with the addition of a very inexpensive bluetooth amplifier.
I posted about this pre-crash, but that post is no longer available so I'll start from the beginning. Came up with this design a few years ago and had the intention of pairing it up with some electronics but had never sourced anything. At that time I had also found an inexpensive 1-DIN, 2-knob style modern stereo that had a small LCD monitor on it's face so went with that instead. I was generally happy with the looks but it always had an annoying hum through the speakers. I should add that my dash had been cut by the previous owner so any modern stereo would work but I wanted it to have the 2-knob design so choices were limited.
I recently ran across a small bluetooth amplifier that would be perfect for this build so decided to resurrect this project. Originally saw the bluetooth board on Etsy for around $95 but decided to shop around and found it on AliExpress for under $11. These are also available on Amazon for around $18 but I was on a mission to do this as inexpensive as possible so went with the AliExpress one. This is a case-less board with a single on-off/volume knob that mounts perfectly alongside my 3D printed faux radio. I was able to make the reproduction knobs work with the board to complete the look, the left knob is functional and the right one is fixed. Sound quality is great with plenty of power, and it doesn't have any more hum like the previous head unit did. It's driving two 6x9 rear speakers and a dual voice coil single front speaker. An additional benefit is that since there is a physical on-off switch and no stored memory settings or clock, there is no need for the yellow unswitched wire connection. This means no phantom power draw like the previous stereo had. IMHO, the whole thing is a simple solution that functions and looks better than the expensive reproduction radios on the market.
Since my dash was already cut I had to get creative in mounting, so I fabricated a bracket that fastens to the rear ashtray brace. If the dash wasn't cut, mounting probably would have been far easier.
If anyone wants to try this solution the 3D printed faux radio is posted on Thingiverse (with over 700 downloads so far) -
https://www.thingiverse.com/thing:3758294/filesNote that you need to use the single hole 1978-1981 style radio bezel with this design. The 1970-1977 2-hole bezel won't work.
Here is the link to the Bluetooth Amplifier on Amazon -
https://www.amazon.com/dp/B086GDNR72There are actually several boards in this style, with some having additional functionality like AUX or USB connections for just slightly more money, so you may want to shop around.