Let's see here... For starters, I think I'd have a barebones starting template. Basically the lowest stats a thing can have while still being a "vehicle" in the
40k sense. This will also let you narrow down the range of possible stats and set prices more easily. So let's say our starting template is something like this:
Move: 6" (technically doesn't fit for something like a drop pod, but meh.)
BS/
WS 6+
S/T/W 5
A 1
Ld 6(?)
Sv 4+
Weapons: None
Special Rules: None
Keywords: Vehicle, appropriate faction-level keywords ("Imperium" and "Adeptus Astartes")
Subfaction Keywords (ex: <Chapter&
gt
: none.
Starting Points: ??? (Not much. Maybe like, 40?)
For Toughness, set a price based on how important that change in value is. Ex: Going from T8 to T9 is a big deal because it means even dedicated anti-tank weapons like bright lances and missile launchers are only wounding you on a 5+. Going from T9 to T10 is less important because it pretty much only matters to S9 and S5. Etc. Totally untested gut feeling values I'd go with:
T5 = +0 pts
T6 = 10 pts
T7 = 25pts
T8 = 45 pts
T9 = 70 pts
T10+ (probably not available in this toolbox. Makes life easier for you. Makes it a bit harder to abuse. If you really want to allow values above 9, T10-13 should probably be relatively cheap increases from T9, but T14 and 16 should probably be a bit more pricey as you're causing anti-tank weapons to wound on 6+.)
Then, charge something like 5 points per additional Wound. So a total of 5 Wounds costs 0 points, (it's included in the template), but a total of 10 Wounds costs +50.
Then, make improvements to the
Sv stat cost X times (Toughness cost) + (total Wounds). Something like:
Sv 3+ = times 0.3
Sv 2+ = times 0.7
So a T7 vehicle with 10 total wounds and a 3+ save (like a rhino) would pay (25 + 50) + ((25+50) x 0.3) = 97.5 extra points for its extra durability. Okay, I see already that my exact numbers need to decrease, but let's keep going for the sake of the general design approach.
Additional defensive rules should probably be calculated similarly to armor save improvements. The rule's multiplier (y) times (Toughness cost + total Wounds). The idea being that Toughness cost + Wounds gives you an idea of how hard the target is to wound and reduce to 0 Wounds, and then the multiplier represents how powerful the defensive rule is. A good invul or to-hit penalty is more powerful on something like an imperial knight than on something like a venom.
To determine the cost of
BS, let's make the
BS value a multiplier on the number of ranged weapon slots the vehicle has. So something like:
BS6+ = x1
BS5+ = x3
BS4+ = x5
BS3+ = x7
BS2+ = x 10
So something like a venom (BS3+ with two ranged weapons) would pay 7 x 2 = 14 points for its
BS. Again, exact values can vary.
For melee performance, do something similar. Set a base price for Strength (probably one based on break points similar to what we did with Toughness), and then multiply that by the unit's Attacks stat. And then multiply
that by a value based on
WS. (WS6+ would probably just be x1). Note that this means you don't directly pay points for the Attacks stat, so you'd want to make sure the multiplier for S5 is at least 1 so that taking a million extra Attacks doesn't end up costing 0 points.
I'd probably just make Movement a flat cost per extra 3". Leadership would also probably be a flat cost and probably quite cheap as it rarely matters for vehicles. Also charge a flat rate for subfaction keywords (gives the vehicle chapter tactics), a flat rate for any additional rule-granting keywords ("death company", "drone"), and a flat rate for the Fly keyword. I'd price any weapon options based on our above formulas for
BS and
WS/Strength.
Oh, and then I'd create a pile of special rules whose prices would probably vary depending on what other special rules or stats the vehicle has. So a "ramming prow" special rule that lets you do mortal wounds on the charge might be cheap baseline, more expensive if you have high movement, even more expensive if you have a high
WS/Strength price, and even more expensive than that if you also have the special rule that lets you charge after falling back from combat. Could probably give these special rules keywords to make it easier to call out synergies like that. Maybe charge a "complication tax" of z points per special rule you added to this monstrosity.
And finally, round your total cost up to the nearest multiple of 5.
Again, the exact numbers I've pitched here are way off, but you get the idea. Costs depend on a combination of factors. High Strength doesn't mean a lot if you can only hit on 6+ with one Attack. BS2+ means basically nothing if you don't have any guns, etc.
