There are many out there at all prices, from $100-$1000.
Don't go real cheap as you want one that does higher temps and therefore pressure.
You DON'T need a real expensive one.
No need for one that you can fill while running. It takes only a few minutes to cool down to refill it, and by then you need the break, so it is not worth the extra expense. You can sometimes find used ones on ebay or craigslist (no relationship).
It is also great for grout, the channels for the porch sliders, and the tiles in the bathroom and entryway (yeah, I guess I am really sold on it).
Again the biggest thing for me is being able to clean the junk without the chemicals on the limited volume on the boat. I can climb down into the lazarettes and clean them out again without choking.