Hmmm - I am checking TireRack.com - an online retailer here in the US, that is very competitive in its prices, and one that I bought my Winter Tires from.
The base 17 size is available for the 528 only. But in that version, I could not find a Max Performance Summer tire - to compare I have used the All Seasons - from Goodyear.
The RFT is the Goodyear Eagle LS2 ($912, 400, V) vs. the non-RFT is the Goodyear Eagle GT ($528, 440, V). So, in the case, there seems to have been some progress in the RFT - as in the wear rating has improved considerably... and it is only about 10% worse. But it is still 70% more expensive.
For the 18 size, you do get Max Performance Summers (where the Michelin Pilot Super Sport currently rules the roost). We can get the Michelin PSS - i.e. the currently best rated tire - for $1108 for a pair of 4 (. For a more even comparison, we can look at similar rated tires from the same brand (I read somewhere, the wear ratings are not so comparable across brands).
So -
Dunlop SP Sport Max GT DSST RFT ($1436, 240, Y) vs. Dunlop SP Sport Max TT non-RFT ($712, 240, Y). The tires are rated similar in wear and speed... but the RFT's are double the price.
Bridgestone RE050 RFT ($1300, 140, Y) vs Bridgestone RE050 non-RFT ($1012, 140, Y) - this is the closest - similar rating and only a 30% difference in price over the lifetime of the tire.
But even with the Bridgestones, the tire to buy is not the RE050. Instead, you can get their latest and greatest - the S-04 Pole Position ($916 , 280, Y). This has double the wear rating and is cheaper than the older RE050 (a circa 2005 tire). And lets not forget - the current benchmark - the Michelin Pilot Super Sport ($1108, 300, Y)...
http://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=148