OED online is VERY* expensive... but many libraries subscribe to the service. if you have online access to a library, check with them; but also be aware that even if they have it you probably have to access it via a proxy server (which they can help you set up).

*Cost: £350+VAT/ US$550 per annum.

but hey, OUP is currently running a 75th anniversary special on the B&M 20 volume-set: only $895 dollar-bucks (this in preparation for clearing the shelves for OED3, no doubt)