Disclosure, I am a lawyer who specializes in contracts. Even if you found a judge who would admit that kind of evidence in favor of an oral contract, all the other guy has to say is that you later changed the terms and it's right back to your word against his. That's the big problem with oral agreements, they are subject to later modification by any old conversation, Email, text or whatever (this is called "parol evidence" in the law, and will be admissible more often than not against oral agreements). Always get contracts in writing. Always. Even if it's just something you type up in a word processor giving it a name, "Personal Services Agreement" for instance, opening with "William Thomas Smith, address, and Theodore Marvin Jones, address, agree as follows on (DATE): Bill will do 1., 2., 3., and in return Ted will do 4., 5., 6." This agreement will end on (DATE), is governed and interpreted under the laws of the State of _________________, represents the full agreement between X and Y concerning services, and may not be modified other than in a writing signed by both parties. Then both sign and date it.
If it's not worth paying for decent legal advice and drafting, it's generally not worth doing. If you call an entertainment lawyer and give them a term sheet of what you've agreed to, they should be able to work it into a decent agency or services agreement economically using a preexisting form. Tell them you are broke and will try to give them referrals if things work out for you. Tell them you don't want them to spend more than two hours on it.
Or just go to the nearest law library during off hours, 9-11AM might be good. Kiss one of the librarian's asses and tell them you are looking for form agency agreements, personal services agreements, or whatever specific agreement, management, recording, production, you are trying to do. Frankenstein those forms up into an agreement, include the terms you and other guy have agreed to, and then take it to a lawyer for review and editing. Shouldn't cost much lawyer time if you do that. You don't need an entertainment lawyer per se, but you do need someone with significant business law and contracts experience. The average generalist courthouse litigator type wont' do you much good. Good luck.