On price differences.
In the Canon world it is absolutely straight forward. Crop is significantly more affordable.
To get the same kind of AF performance that is available in an APS-C body like the $1,350.00 7D2 in a Canon full frame body, one needs to spend $2,200-4,000 (5D3 or 5D4)
Glass is no different.
EF-S 18-135mm STM offers better image quality and broader zoom range than 24-105mm L at a lower cost.
EF-S 10-18mm IS (or 10-22mm) vs. EF-16-35mm f/4L IS. Price difference is considerable with the same field of view. If we go back to the days of the 17-40mm f/4L, the EF-S lens was wider field of view and sharper throughout the zoom range.
Crop lenses CAN and ARE being made lighter weight and at lower costs. This is a fact of physics. If one chooses to adjust the rules to fit your argument, sure you can prove that a specific FF lens is smaller or more affordable than a specific crop lens, but that's on you to have made the criteria fit your own argument. It does not jibe with physics or reality or the whole picture. Those rare exceptions frankly help prove the rule.
The debate of which format has superior image quality, (or more to the point, how important the actual difference is) may go on, but the cost differences can not really be toyed with IMHO. And certainly for some, they also can not be ignored.
Canon is the king of cheapie but goodie lenses, they are the market leader for a reason.
as for the newer EF-S competing with FF lenses, not happening and TDP proves it: http://www.the-digital-picture.com ...omp=0&FLIComp=5&APIComp=3
the FF image is considerably crisper at it's peak setting.
As for the Physics comment, this doesnt hold true due to the flange distance of the mirrorless cameras. Consider the closest matches and you can see size differences. Sony's 12-24 f4 is closely comparable to the sigma 12-24 f4 and Canon 11-24 f4. Good amount smaller and less than half the weight.
sony 16-35 f4 is shorter and lighter
sony 16-35 f2.8 is shorter and lighter
sony 24-70f4 shorter lighter
loxia 21 f2.8 compared to EF mount distagon 21 f2.8, much lighter much smaller
sony 28 f2 compared to canon 28 f1.8 good bit lighter and a good bit smaller
sony 50 f1.8 little BIGGER similar weight. At this flange distance, the flange distance starts losing effectiveness. The lens uses a DSLR design. Either way, both lenses are fairly featherweight.
sony 85 f1.8 little bit smaller and lighter.
I havent mentioned voigtlander/tokina/batis lenses either, many are optimized for size and performance.