Right, insulation isn't that expensive, it's mostly labor. So laying down rolls in the attic is cheapest (held by gravity), then tacking rolls up into the joist

Right, insulation isn't that expensive, it's mostly labor. So laying down rolls in the attic is cheapest (held by gravity), then tacking rolls up into the joists in a crawl-space probably comes next. Opening walls or vaulted roofs is much more intensive. Another problem is older framing might use 4" studs or rafters and you'd really want 6-8" to have more space for adding thick insulation.