There is a definite range for something like that. One thing that concerns me right off the bat is the 12k part of it. In Beijing it is usually 10k that is offered, and that 10k actually happens to be gold plated and not real 10k.
If the strand is purchased as 7-8 mm, the actual size is going to be 6.5-7.5 mm, with about 75% of the pearls falling within the 6.5-7 mm range and the other 25% falling in the 7-7.5 mm range. There is a big difference between material size 7-8 mm and strand size 7.5-8 mm in both size and value. The finer goods are usually separated into half-size ranges in that size, so you would want to look for 7.5-8 mm.
As far as the prices go, the range could go from as little as 50 RMB to over 1000 RMB. Round and white doesn't really describe much. What is the degree of round? You won't likely find loose-pearl, true round strands in Beijing. Shape, size, luster, spotting ... all combine to determine the value. Your negotiation skills will determine the cost.