I don't have an answer, but I doubt you can prove its the most fiscally effective solution.
I'm sure there's been studies on the costs of doing this. These are just off the top of my head.
1 - finding and sending them home. This will be huge. There're not all from Mexico, not always an easy/cheap trip. Cost of finding them will put cost pressures on local law enforcement. Cost to detainment while you send them home. Some you won't be able to prove to the receiving country that actually is their home which increases detainment time, sometimes indefinitely.
2 - lost low cost labor would increase business costs resulting in inflation and business failures. This may also be huge. Its an unknown economic shift.
I'm sure there's been studies on the costs of doing this. These are just off the top of my head.
1 - finding and sending them home. This will be huge. There're not all from Mexico, not always an easy/cheap trip. Cost of finding them will put cost pressures on local law enforcement. Cost to detainment while you send them home. Some you won't be able to prove to the receiving country that actually is their home which increases detainment time, sometimes indefinitely.
2 - lost low cost labor would increase business costs resulting in inflation and business failures. This may also be huge. Its an unknown economic shift.