Very easy way to cut the cost down massively. As deportation isn't a punishment there is no need for a trial and an immigration hearing. No documents? No visa? No status? Deport. There is no reason at all we should be providing any sort of judicial hearing for illegals when being deported. There is no excuse "I misplaced my papers" or "ohh wait here I am a citizen!".

Find them. Handcuff them. Send them to the nearest deportation center. Bus's leave every day likely wait is 48-72 hours tops.

Just cut that 187 billion down to 30 billion, now put the rest into the military securing our border and problem fixed.