It would help if you told us in what context you wish to use the word "corpus," but it's probably a bad idea to use it to mean an amount of money.
The word is a legal term of art for the property held in an estate or trust. That's all property, real and personal, which includes many more categories than money. For a definition that the Internal Revenue Service of the Unites States uses when it's prepared to tax the estate of a recently deceased person go here.
"Corpus" is the Latin word for body, and it should be no surprise that it shows up in many different legal and medical terms that will compete (if only slightly) with your intended use.
Amounts of money have different names in different economic spheres. "Endowment" for universities and foundations; "reserves" in banking. If possible, choose the word specific to your context.