“Hi, you know who you called; leave a message, maybe they’ll call you back. Then again, maybe they won’t. That’s how life is. Point is, you’ve done what you can. Have a nice day.”
“Good afternoon. You have reached the office of [your name]. I will be out of the office beginning on [date] and will be returning on [date]. Please leave a brief message with your contact information, and I’ll be sure to get back to you as soon as I return on [date]. If this is an emergency or you need to speak with someone before I return, please contact [name of colleague/supervisor], [their job title], at [their phone number].”

Recording the message yourself doesn’t mean it can’t be done professionally. You can still get studio time with an experienced audio engineer. Studio time can cost $60-$100 per hour, which may or may not come with an engineer. If you need to hire one, their rates are usually $100-$300 an hour. Mind you, their feedback, professional experience, and editing capabilities are typically well worth the extra expense.
Friends and colleagues speak to each using first names only. So do people of authority. They do not call each other and leave voicemail messages asking for Mister, Miss, or Mrs. Therefore, when you call a person you want to do business with and you leave a voicemail message, refer to them by their first name only. Don't say mister, miss, or misses. Don't say their last name. Begin your voicemail message by saying only "hi/hello" followed by the person's first name. Or, you can even forget the "hi/hello" and just say the person's first name. That is how you show confidence and authority and separate yourself from weak salespeople.