Any old cheap audio amplifier. Preferably not your $5000 home theater though.
Then do this....
Pull the Satellite finder apart and find the wires that connect to the back of the meter. NOTE: Buy one with an analogue meter not a digital display.
Connect the input to the amplifier across the meter movement, you may get better results if you cut the sires to the meter???? Test it?
Connect your Satellite finder to your old pay TV dish.
Fire it all up and point the Pay TV dish towards the sun,
If all goes well you should hear something through the speaker.
You have just built a very rudimentary Radio Telescope,
I have heard of people using a big arse old C band dish which are not too hard to find if you hunt getting a signal fomr Juipiter
using the same method. Just replace your little Pay TV dish with the big arse C band dish.
Good luck aiming at Jupiter though :)
Old C band dishes are about 2M in diameter and are pretty much obsolete these days. You should be able to source on for not much money/
Oh one final thing.
You will need to power up your block converter. Thats the little box that sits in the focul point of your dish.
This is probably the hardest bit of the project.
I cant advise you as the method id to some degree dish/block converter dependant.
Ask google, your local satellite TV guru or...
If you send me the exact model of the block converter I will try to help.
Hope you have fun with your first DIY radio telescope.