There is an alternative: locking down until testing can be significantly ramped up. This wouldn't need to take more than a month or two. The cost to test even everyone in the population on a weekly basis is much, much lower than the cost of being locked down, and once that infrastructure was in place, other measures could be dropped, because we would know and could isolate only those who are infected (symptomatic or not).

Edit: I should add that ramping up testing may take longer than that. I'm not an expert; just going by what I've read. Even so though, we should definitely aim to scale up testing as much as possible; the better our testing, the less restrictive and long-lasting isolation measures will need to be.