Step 4: Figure out the Cost

Cost depends on the type of trap. Calculations are given below for the three basic types.

Mechanical Trap

The base cost of a mechanical trap is 1,000 gp. Apply all the modifiers from Table 2–2 for the various features you have added to the trap to get the modified base cost.

The market price is the modified base cost × the Challenge Rating + extra costs. The minimum market price for a mechanical trap is 100 gp per +1 CR.

After you have multiplied the modified base cost by the Challenge Rating, add the price of any poison or alchemical devices you incorporated into the trap. If the trap uses one of these elements and has an automatic reset, multiply the poison or alchemical device cost by 20 to ensure an adequate supply.

Multiple Traps: If a trap is two or more connected traps, determine the market price of each separately, then add those values together. This holds for both dependent and independent traps.

Magic Device Trap

A one-shot magic device trap costs 50 gp × caster level × spell level + extra costs plus 4 XP × caster level × spell level. Magic traps with the automatic reset feature cost 500 gp × caster level × spell level + extra costs plus 40 XP × caster level × spell level. If the trap uses more than one spell (for instance, a sound or visual trigger spell in addition to the main spell effect), you must pay for them all (except alarm, which is free).

These costs assume that you are casting the necessary spells yourself. If you are hiring an NPC spellcaster to cast them, see the Special and Superior Items section of Chapter 7 in the Player’s Handbook for costs.

Magic device traps take one day to build per 500 gp cost.

Spell Trap

A spell trap has a cost only if you hire an NPC spellcaster to cast it. See the Special and Superior Items section in Chapter 7 of the Player’s Handbook for these costs.