i got a second hand extreme arb (bright orange) from ebay £90. its gotta be twice the thickness. although, a front arb from a classic doesn't look much different to the rear mounting wise. it may be that you can fit a front arb to the back with different drop links or by moving the mounts on the axle slightly. a little bit of effort but much cheaper and the front arb is a similar thickness to the extreme ones. i think the 110 arb's are the same thickness as the rrc, not sure about 130's. it does make a big difference on the classic. mine has much less body roll.