Ok
Code:
Firearm Accessories
Apostle 2 sp —
Bandoleer 5 sp 1 lb.
Bullets (20) 1 gp 2 lb.
Cartridge box 8 sp 1 lb.
Percussion cap 1 sp —
Powder horn 1 gp 1/2 lb.
Ramrod, iron 1 sp 3 lbs.
Ramrod, wooden 5 cp 1 lb.
Swine feather 2 sp 2 lb.
As far as what you can afford with 450, that is the list of accessories. (Silver bullets are 1 GP each btw). With a flintlock, you need apostles (Single shot of powder in a wooden holder) and a bandoleer to carry them (12 in a bandoleer), as well as a bullet. A powder horn has 12 shots of powder.
I believe only muskets use cartrage boxes, which has everything in it, and gives you a +2 on your munitions check (1 box has 20 cartridges). Not sure if they also need the apostle, but don't think so.
Supposedly, firearms come with a wooden ramrod, but that again is vague.
Swine feather is a tripod like setup that gives you bonuses to hit if you're placed on two handed firearms.
As far as guns, non-masterwork, sorted in order of damage (All are x3 crits)
Light Weapons
Holdout Percussion Cap 90
Light Flintlock 90
Light Percussion Cap 120
1 Hand weapon:
Double Barrel Flintlock 200
Double Barrel Percussion Cap 250
Purcussion Cap Revolver 500
Heavy Flintlock Pistol 130
Medium Percussion Cap 180
Heavy Percussion Cap 220
So, if you insist on Masterwork, you can get a Heavy Flintlock, though a heavy percussion cap might be a faster load.