Generally, I'd say $40 is too much to pay. SEs aren't in my view particularly collectible. Aside from being the first 68000-based Compact Mac that uses ADB and takes an internal HD, there's nothing distinctive about it.

If you specifically want an SE, and you can't find another one cheaper without having to pay shipping on it, and you have your own keyboard and mouse available, and you don't mind the possibility that you'll only be able to use 800k disks with them, then go ahead. Otherwise, I'd say offer him $20 for both, or wait for a better deal.

Best,

Matt