Cool! I had codex have a go at calculating "effective price" on a few items, that prices in the assembly labor, and then also calculates the delta between price and effective price. Obviously very depended on how you value your time, but here are some items at $30/hour:

BRIMNES storage bed + headboard, Queen $549 + 320 min labor = $709 (delta: +$160 / +29%)

HEMNES 8-drawer dresser $380 + 236 min labor = $498 (delta: +$118 / +31%)

STORKLINTA 6-drawer dresser $250 + 224 min labor = $362 (delta: +$112 / +45%)

SLÄKT storage bed, Twin $450 + 212 min labor = $556 (delta: +$106 / +24%)

BRIMNES 3-door wardrobe $250 + 189 min labor = $344.50 (delta: +$94.50 / +38%)

ALEX drawer unit: $95 + 96 min labor = $143 (delta: +$48 / +51%)

BRIMNES cabinet with doors: $99 + 75 min labor = $136.50 (delta: +$37.50 / +38%)

KALLAX 2x4 shelf unit: $65 + 39 min labor = $84.50 (delta: +$19.50 / +30%)

Formula: effective price = sticker price + (estimated assembly minutes / 60 * hourly value of time).

I was surprised by how similar the % diff is across the board.