Well since its lapped, its worth LESS. Lapping if done correctly is fine but voids the existing warranty. Lapping if done incorrectly can damage or ruin the CPU.
Also, to give any kind of value we need the following:
When was it purchased?
What stepping?
Has it been overclocked?
What temps has it been exposed to?
Of course, you could lie, but that would defeat the purpose of getting an accurate value.
Humor me.