[dmjlambert]

Your best option on a low budget and for occasional use is leave the AM radio and its speaker right where it is in the dash and get a nice portable Bluetooth speaker to attach under the dash or sit on the hump or stuff slightly under the seat. Bose Revolve series speaker fits in a large cupholder and has room-filling sound. Other people have used JBL speakers and other brands.
I bought a non-working AM radio for mine and got it working with some sprays of Deoxit D5, and plan to repair my cut-up dash and get the radio going with a reproduction AM radio speaker, so everything will be working as original, and I have a completely independent blasting stereo under the seat I use with bluetooth.