From the inclinatioroma vcoins store:

TIBERIUS & CALIGULA AS CAESAR AE30 CARTHAGO NOVA SCARCE DUAL 

CARTHAGO NOVA, SPAIN AE30 TI CAESAR DIVI AVGV F AVG P M, 
Laureate head OF TIBERIUS left/C. CAESAR TI. N. QVINQ IN. 
V.I.N.K. Bare head of Caligula left. RPC 182, SNG_502, SGIC 
337, Cohen 245, 3. 13.6 g. Near VF with full legends, good 
portrait detail and even brown patina.  Some surface 
roughness. 
SCARCE DUAL PORTRAIT ISSUE OF SECOND AND THIRD EMPERORS. 
 
Carthago Nova was the only mint in the Empire that struck 
coins in the name of Caligula as Caesar.

Price 
  US$ 265  euro 220.22
 £ 152.07
 AUD$ 372.86
 CHF 347.17
 CAD$ 309.36

Rates for 3/24/2006