I use a Sekonic 398 Studio Deluxe.
Not particularly cheap new but they have been making them forever so the older they are, the cheaper they can be found.

I bought mine new and it is right on but I have heard that selenium meters can lose accuracy over many years. Rather than poking and hoping to get a good, cheap one on ebay I tend to agree with Jeremy, the wisest solution might be just to carry spare batteries for your other meters.

If you go for a selenium remember that they are also powerful magnets, so be careful to keep it isolated from any digital equipment that you might have and don't put it in your pocket next to you credit and atm cards.