It's not an issue in terms of cost, it's probably a tiny fraction of the amount we pay to lazy UK residents.I think benefits for EU imigrants is a complete non-issue and is only on the table because the Tories have talked it up for several years when chasing cheap votes.
The vast majority of EU migrants come to the UK because it is relatively easy to get a job here, we are a largely tolerant and multi-cultural country with established communities from most countries and nearly everyone has English as a second language (or want to come here to learn it).
If it really is an issue (it isn't) then it can easily be sorted out domestically by limiting benefits until you have contributed x amount.
It's an important issue of principle though. The concept that one can just claim money from the pockets of residents in any European country one wishes is just ludicrous.