Forgetting for a moment that the total sum of a 12th level character's gear is supposed to be somewhere around 88 k, let's assume a 12th level character is moderately equipped with gear and has 120 k extra assembled.
Does he buy a:
a) Commander's Ring (+2 resistance bonus to saves; +2 deflection bonus to AC; feather fall, knock, wall of force, and daylight 3/day; and knowledge of other ring bearers within 100') $120 k
b) Diviner's Staff (identify, locate object, locate creature, analyze dweomer, and vision by charges [50 max]; and +1 competence bonus to knowledge checks) $137 k
c) Eye of Winking (immune to detect thoughts and mindreading; reflect charms and compulsions; immune to all spells, spell-like abilities, and supernatural effects for 1 round once every 10 days) $120 k
d) Ring of Limited Invulnerability (HD all become d12; Natural Armor +5; 1d8+5 negative energy touch attack at will; Fear Aura 60' radius (Will DC 24); Paralyzing Touch (Fortitude save DC 24 at will, duration permanent); DR 15/+1; Immune to all Cold and Electricity attacks and spells; Immune to all mind affecting attacks and spells as well as necromancy spells, spells that cause fort saves, spells that polymorph, spells that paralyze or stun; Immune to all poison, sleep, disease, death effects, ability drain, energy drain; Immune to all critical hits, sneak attack, ability damage, and subdual damage; +2 Unnamed bonus to Intelligence, Wisdom, and Charisma; and +48 to skills; if destroyed in some manner the character is not immune to, the character reappears 1d10 days later unless the ring is destroyed; the ring does not have to be worn for any of these effects to continue) $120 k
Sign me up for that bargain.
Here's a question, please give me an answer to this. Does becoming a lich affect the usage of the way the term "level" applies to you?
i.e. does it make you more powerful than the average example of a character your level?
does it make you capable of overcoming challenges that might normally require a higher level character?
does it give you abilities which when added to your current abilities might make you be considered as slightly more formidable than other members of your party of equal level?
If the answers to any of these are yes, then the lich needs to have his level changed just so the DM knows the correct average party level in relation to CR's and XP awards. If the group still wishes to call him a 12th level character, that is fine, as long as the DM understands that effectively as far as the D&D rules are considered for play balance at particular levels he is actually closer to an X level character, and as long as the players understand when they reach X level, they will have similar powers as well.
For the record, as I've stated before, I believe Artoomis's suggestion to be the most reasonable one that both allows the transformation and all these powers, but also keeps the character in line with both the powers of the party and the powers of similarly leveled characters from the stand point of how the game (XP and CR) considers the PC.
Edit: Just flipping through my DMG for other price comparisons, how's this? Immunity to sneak attacks and critical hits? 36 k That + DR 5/+1 (not 15/+1)? 81k That + Cold Resistance 10 (not cold immunity)? 144 k We're already well over price and haven't even gotten to 1/10th of the abilities. Lichdom cannot be treated as an item fairly. It simply cannot. I must be a class or a level equivalent.