This should give you a ball park of what the swap could cost:
http://www.hotrod.com/articles/hrdp-1103-small-block-or-ls-engine-install/
5.3L SWAP WITH
CARB
Used 5.3L engine with front drives and accessories $180
S&P motor mount adapter plates $100
GTO oil pan, pickup, and windage tray $100
TrailBlazer V8 exhaust manifolds $125
Comp Cams Mutha Thumpr cam $400
Comp Cams beehive springs and retainers $315
GM single-plane carb intake $380
Holley 750-cfm vacuum-secondary carb $270
MSD coil pack control box $310
14-inch open-element air cleaner $25
GM 4L80E flexplate, spacer, and bolts $200
TH350 detent cable and bracket $45
Holley “blue” electric fuel pump and regulator kit $132
TOTAL
$2,582
5.3L/4L60E SWAP WITH
EFI
Used 5.3L engine with front drives and accessories plus 4L60E trans $1820
S&P motor mount adapter plates $100
GTO oil pan, pickup, and windage tray $100
TrailBlazer V8 exhaust manifolds $125
Comp Cams XFI cam $400
Comp Cams beehive springs and retainers $315
Used ECU $100
Reflash ECU $300
Used drive-by-wire pedal and solenoid $150
Used MAF meter and air cleaner $100
30 lb/hr fuel injectors (set of 8) $250
4L60E early Nova trans crossmember $175
Shorten driveshaft (Wenco) $75
Rock Valley EFI-style stamped-steel fuel tank and electric pump $725
Abbott Cable-X box $325
Miscellaneous wiring and plumbing $300
TOTAL $4,520