All the quotes are a little on the high side, but I suspect there is a valid reason for this. Is this a complex roof with tiles or slate? Is it a double story, or is site access difficult? Also, long cable runs and adding a smart meter adds to the cost.
In regards to the difference between the Panels, The REC Alpha Pure-R are extremely good and definitely the best panels available. Very low degradation and great performance in hight temperatures.
However, the Trina Vertex panels are great value for money and will do a great job if you cannot justify the extra cost. The REC370TP4 and SunPower P-series are both similar to the Trina panels in performance.
Actually, I didn’t take note of the out-of-pocket prices you posted. They are maybe 5 to 10% higher than average. Although, when I think about it, adding the smart meter takes extra time, plus the cost of the meter, so overall it’s pretty reasonable. However, the first quote is definitely above average even for premium panels.