It is good to hear that some else leaves the house without their helmet.
Go to a thrift store or good will and look through the bike helmets and maybe try one on. If you don't want the used helmet then just note what make and model it is and then go buy it at your LBS or order it on line.
If you buy used, then you don't know the history of the helmet so it could be defective but my thinking is a defective helmet is better than no helmet at all.
Also playing chicken with a semi is a bad idea even if you have the best helmet available.