Maplin were doing one for £50ish that accepted SD mem cards. Have a look on the website.
There is also one "Yakumo - MP3/WMA Car Stereo - with SD & USB Slot" from amazon ( there were sold out when i last checked) i bought one and its great little unit, cost £75 so pretty close to your target..
has usb slot, sd card slot and can play mp3 from cd or usb and sd but it can ALSO record radio to the usb key! so if you like a track wack the one touch record and job done...