i have photo shop elements( under $100) and you do it with multiple process there. you just type in what you want, pick the color and opacity and size and then it will process what ever photos you select. what ever you chose to use, you would need something with a text option and something you can vary the opacity of. imo a better option is downloading to someplace like zenfolio..there you can make your own watermark or use their's and it doesn't permanently mark them, just when you use the link from there to post it has the watermark.
if you want to permanently mark them the photoshop would work fine, otherwise you have to have a watermarked and non watermarked copy since once it's marked you can't unmark it very easily.