Worried now about alterations costs

I bought this gorgeous dress as a sample off the rack. It’s about 2 sizes too big (16), it’s clipped here but still had a significant amount it could go in. Tried to stuff myself into the size they had that was smaller (10) and couldn’t breathe so that wouldn’t work. The associate made it sound like alterations would be easy peasy, but the more I read, I see costs upwards of $1000k for major alterations. From those of you that might know things about alterations, is this a) doable? Or is this going to probably be a nightmare?b) going to likely be extremely expensive? c) will I need to have the skirt taken in around the seams of the bodice? I’m not sure if it’s a thing that needs to happen.

I need to brace myself for what might be coming