While I accept your example of keeping the same prices, IMHO it would be preferable to use standard costings where possible.
OK, I have done a little research, and here are some details (and possible stats) for the variants I could find (note I have ignored the Spartan and Hellfire which seem to be from a previous era). I have left off the common stats (AV, armour 4+RA, TRA, 25cm move etc). Enjoy:-
Standard LR     FF5+, CC6+,
1x Heavy Bolter,     AP4+ (30cm)
2x Twin Lascannon    AT4+ (45cm),
Transport 2/1
Crusader LR     FF5+, CC6+
1x twin Assault cannon,   AP4+/AT4+ (30cm)
2x Hurricane Bolters,    (small arms) (EA+1)
Transport 3/2
http://wh40k.lexicanum.com/wiki/Land_Raider_CrusaderRedeemer LR     FF5+, CC6+
1x twin Assault cannon,   AP4+/AT4+ (30cm)
2x Flamestorm cannon,    AP3+    (30cm) IC
Multi Melta         MW5+    (15cm)
. . . . and small arms MW (EA+1)
Transport 2/1
http://wh40k.lexicanum.com/wiki/Land_Raider_RedeemerHelios LR      FF5+, CC6+,
1x Whirlwind Missile,    BP1
2x Twin Lascannon      AT4+ (45cm),
http://wh40k.lexicanum.com/wiki/Land_Raider_HeliosPrometheus LR    FF4+, CC5+,
1x Storm bolter,       (Small arms)
4x Twin Heavy Bolter     AP4+ (30cm)
Transport 2/1, Enhanced Command (a commander added to the tank can control other formations up to 30cm away)
http://wh40k.lexicanum.com/wiki/Land_Raider_PrometheusThe following two variants probably need to be higher costs due to their additional firepower. They are also rare, and the Ares is aparently limited to Dark Angels
Terminus LR     FF5+, CC6+
2x Lascannon,        AT5+ (45cm)
3x Twin Lascannon      AT4+ (45cm)
If four '1's are rolled, the power plant overloads blowing up the tank.
http://wh40k.lexicanum.com/wiki/Land_Ra ... inus_Ultrahttp://www.games-workshop.com/MEDIA_C....der.pdfAres LR      FF4+, CC6+,
1x Assault cannon,      AP5+/AT5+ (30cm),
2x Twin Heavy Flamer,    AP3+    (15cm) IC
1x Demolisher cannon     AP3+/AT4+ (30cm) IC
Invulnerable Save
http://wh40k.lexicanum.com/wiki/Land_Raider_Areshttp://www.games-workshop.com/MEDIA_C....res.pdfAlso the Wiki
http://en.wikipedia.org/wiki....40,000)