For vibrochamp I wouldn't use a C Rex, or if I did I would mix it. For true Champ tones you could use an exact copy of the original Jensen C12N (not the new reissues), which is the Red, White and Blue.
I personally favour the Texas Heat - it gives you all the Fender tones and has a great distortion on top. I have one in my Blues Junior and it roars. Although this is heresy on these boards I wouldn't bother with British style speakers in a Champ, in my view they just don't cut it with the Blackface circuit.
139 for a 1x12 and a C Rex is OK - the C Rex goes for about £50 from Blue Aran and you can get unloaded Blackface Deluxe style cabs off ebay for £90.