2.5mm port user here too. These cabled releases are ubiquitous and cheap; I got one off of eBay years ago and have used it with 3 brands of camera I have owned so far. It's a simple one that just features half-press to AF and lock press for bulb; enough for my simple needs. I think it was $15 shipped. You can also get quite sophisticated ones for time-lapse shooting and stuff like that for not that much money; check out Rico's article above for lots of info.