Easier to just replace the head unit. You will need the face plate that fills the gaps either side of the new head unit as the replacement unit isn't as wide, the aerial booster and probably to swap the red and yellow power wires over. (loads of posts about this)
I got a jvc 811 for about £120, it's not the greatest design and quite annoying to use, but it does the IPOD, MP3 players, hands free bluetooth, takes usb memory and the illumination on the screen and buttons can be changed to nearly any colour to match the dash.