Yeah, I don't really think they are gonna charge you a lot more to weld a flange to stainless than what they would charge for steel on to steel. Just remember, if you do have the flange welded on you compromise the integrity of the stainless steel at the bead of the weld. In other words, it will rust in time. I would suggest you save for a little while so you can afford to get the weld done as well as getting the pipe powder coated both inside and out side, if possible, with a high quality and heat resistant powder coat.