Options
3) Contractor - with at minimum a 25% wage premium to cover self-employment taxes, plus (depending on where you are) some form of city and state taxes, medical insurance, general liability insurance, unemployment and worker's comp, plus the extra time and admin costs to manage all that. If you can lock up a long-term contract with early-termination fees (sounds like a mobile phone contract!) that is ideal, but if not then you need to evaluate the risk of unemployment while looking for the next gig. Higher risk = higher pay.
4) Negotiate higher pay - not offering a 401(k) means $18k is subject to taxation, so (depending on marginal tax rate) ask for $5k more. With the stipulation that you'll take a $5k pay cut if they offer a 401k.
5) Tell 'em they are idiots for not offering a 401(k) and that you'll take the job only if they offer one. Fidelity, Ubiquity, Vanguard and others offer plans that cost a few thousand per year in admin fees. The company doesn't have to match, so their total cost would be less than in option #4.
6) Keep looking... honestly, a company that has 3+ non-owner employees has no good reason to not offer a 401k plan.