Perhaps OP is only looking to answer the question of illegal immigration and it's financial impacts, but I have to consider the context of the question. Is it a drain or a benefit? Hard to tell really, as it's illegal and off the books. However, we do know that it in no way compares with a 716 Billion dollar US "defense" budget.

For instance, Venezuela is a country of people with a democratically elected leader who want to stay in their own country, yet the US government is pushing for their own agenda. To say that we need to block immigration to the US because of the financial impact yet also say that we should use the US military, which has a far higher economic impact, to "help" the people of Venezuela is hypocritical in the least.

Also, should a community, nation, region, tribe, what have you - have the right to sovereignty and the right to refuse individuals in order to preserve their own culture and values?

I am personally not too concerned about illegal immigration and it's effects upon my livelyhood, I am however concerned about the US and NATO bases plastered across the world and their foriegn wars and interventions causing mass immigration.

These are my thoughts, hopefully not too off-topic.