I've never seen any studies done about what the impact of illegal immigrant labor is on wages across the board, but I can tell you that it just isn't the menial tasks that they are doing that drives down wages. Even my wife who's an RN sees the effects of their cheap labor. It took her about 6 years to start making the same wage she made in Deleware, and she does the same job out here.
The biggest impact on illegal immigration I hear about in Tucson is the burden it puts on the only trauma care hospital in the city(used to be 2 or 3, but they shut down because they were losing so much money). After a recent particularly bad accident involving illegals, when a truck overturned carrying 24 of them and 4 were killed with others seriously injured, the hospital made it a point at the news conference to mention how much money it was going to cost the taxpayers to treat the patients. Just this one incident alone was said to cost $500,000.
As far as how easy it is to get across the border, I don't think it's a walk in the park. They die by the hundreds out in the desert as they try to walk from the border to places like Phoenix. Not an easy trek by itself, and made more dangerous by the heat and lack of water.
