Where can I find a scatter plot of welfare spending (per capita, % of spending, or % of GDP) vs. immigrant rate (per capita, or % of population)? By state or by country would be fine. I tried to search, but came up empty:
If you're looking into the "welfare magnet hypothesis", there are plenty of papers, e.g. this has a reasonably close plot what you ask for:
with the commentary
An essentially null effect also emerges when looking at spending on unemployment benefits as a percentage of GDP . Data from 19 EU countries for the period 1998–2008 show a small positive association between spending on unemployment benefits and immigration flows for immigrants from non-EU origins (see Figure 2). But the effect was essentially zero after taking into account that immigration itself affects the level of public expenditure. Factors such as income, unemployment rates, and the presence of previous immigrants in the receiving country were instead the major determinants of immigration flows.
-  Giulietti, C., M. Guzi, M. Kahanec, and K. F. Zimmermann. “Unemployment benefits and immigration: Evidence from the EU.” International Journal of Manpower 34:1 (2013): 24–38. Online at: http://www.emeraldinsight.com/journals.htm?articleid=17085869&show=abstract
Here is a more complete answer which includes all types of welfare, not just unemployment benefits, and 50 data points, not just a dozen. It also has a trend line which shows no correlation.
http://www.pewhispanic.org/interactives/unauthorized-immigrants/map/population-share/ (not used)