Honestly, radio transmission should be your LAST option. Despite their prevalance they are very unreliable and have quite shoddy performance. If you have the funds to get a new player do it. Also, many companies now offer products where you can buy a line in imput that will allow you to hardwire your iPod to your car stereo without buying an actual new stereo. I'm not quite sure who sells this but i'll post back if i find some (i believe it's more money than a 3rd party radio transmitter but cheaper than a new deck)
To answer your question, in my dad's car there is a line in provided that i connect to via mini-stereo cable (Honda Element), my step-dad's car via Tape Deck (Mazda Miata), and my mom's via
Scosche FM transmitter (Honda Civic, only using this because it was cheaper than hardwiring/ the car doesn't have a tape deck/the car's leased

)