We aren't talking about 'as things stand', we are talking about the effect this policy is going to have, isn't it supposed to be a deterrent and therefore reduce illegal crossings? Surely it is pretty simple to forecast a best/worst case scenario and project cost based on that? Do you wonder why they haven't produced and published that alongside the policy?
Surely you need to see this before you decide whether it is a good idea. Would you support this policy even if it ends up costing more?