Remember that even if you have the money for a 5D3, EF lenses of the equivalent quality and focal length compared to those on crop cost significantly more. Overall, going FF costs alot more than the same route on crop.
Take for e.g.: the EF-S 17-55 is the general multipurpose lens for crop (and many have said this one is a hidden L lens). The equivalent is the very reputable EF 24-70 on FF. The price? 17-55 costs $1.5k new. 24-70 costs 2.1k. That's 40% more.
For UWA, you can get great quality with the EF-S 10-22 on crop, or you can get the EF 16-35 for FF for superb quality. There's a difference between the quality, but check out the price difference too: 10-22 costs 1.1k new, and the 16-35 costs 2.5k. Over double the price.
Then also, because the crop has a 1.6x "extending effect", you benefit from primes too. An EF 50 1.2L mounted on a crop gives an equivalent of an EF 85 1.2L on an FF (it's about the same field of view. Quality is great too since both are L lenses). The difference in price? 2.4k vs 3.5k. Almost 50% more.