I've tried a number of different masks/respirators trying to find a good one that is reasonably priced and up until now found them lacking. (I've seen the old threads about this, but didn't find this mask mentioned.)
I just spent the day welding with a new one and it blows all the others out of the water and doesn't cost an arm and a leg.
Its a 3m 7500 half mask respirator. It comes in different sizes, so you can get a decent fit (I got the Large). Its a low profile mask and fit under my hood with room to spare. It has different filters available so that you can get one appropriate for what you're doing. They have a number that are recommended for use with welding.
Its a soft silicone mask so it seals well and is comfortable. The biggest plus for me is that the exhaust valve is at the bottom of the mask. I've always had problems fogging my glasses and my hood. With the exhaust going out the bottom, the hood stayed clear.
I couldn't smell a thing when welding and grinding. (I used the 2097 organic vapor relief filter.)
I got it on Amazon and it was $24 for the mask and $8 for a set of filters. So, I thought the price was great for a high performance respirator. I don't yet know how long the filter will last.
Just wanted to post my experience so that others looking for a respirator know this one works well.