[ericgrau]

Ugh hate that trick. It makes sandstone. A titan can't break free from sandstone?

Anyway, C729 / H729-2
The standard pricing is 40 gp (2000/50 = 40) * effective-bonus * effective-bonus. So for +1 flaming (1d6 fire) it's 160 gp. For +1 flaming burst (1d6 fire, plus 2d8 more on a crit) it's 360 gp.

Now to metagame this a bit: These arrows suck except at high levels or except when saved for major foes like BBEGs; normally you get an even nicer bow first. So I'll discount them to balance for low level play, make them alchemical like you seem to want, and prevent (ab)use at high levels. I'll say 75 gp for +1d6 fire damage, and this may be multiplied by a crit. These alchemical arrows may not be enchanted; even when fired from a magic bow they don't deal extra magical damage. They also set fire to easily ignitable things like dry brush, tinder, curtains, etc., but not most other objects and creatures.