Technically there's no such thing as a 'factory C+' board. The RP11A/SP11A boards were designed for the IIC and the later IICs also had them. All C+s are IICs with the + mod done to them. The only difference with 'factory C+s' is that this + mod was done at the factory during their production phase rather than at a later stage, and the ones built from late 83 onwards will probably have a 105PT. Anyway.
Price wise I'd rank them as follows from worth the highest to the lowest.
(K=Coliseum D=Simul, H=100W, S=60W, R=Reverb, G=Graphic)
KRG
DRG
HRG
SRG
KG
DG
HG
SG
KR
DR
HR
SR
K
D
H
S
Then based on that you can add in the following for more value for each of the following:
105PT worth more on the US Voltage models (obviously not the coliseum that has its own crazy PT). Export IIC+s will not have the 105PT. Really doesn't make too much difference which transformer IMO but people will argue over this...
Long chassis worth more.
Hardwood Cabinet with Wicker Grille worth more
Switchable +/++ worth crazy money
So to answer the original question, a DRG is second highest on the list. Minus some value since the reverb is missing. This would raise alarm bells for condition for me and I would check it out and grab internal pics of the chassis before buying if possible (if you're buying). If you're selling then it's worth what someone will pay but it'd be on the higher end of the spectrum because it's a simul and it's got a GEQ.
Hope that helps!