In determining spousal maintenance or child support, attorneys often find themselves having to prove payment for costs of goods or services. How is this accomplished?

Imagine, for example, trying to enter into evidence proof of payment for extracurricular activities. You have a receipt for $1,800 for gymnastics classes, and an email confirmation for private figure skating lessons in the amount of $3,600. Your client is prepared to testify as to enrolling the parties' children in these activities and paying for the classes and the coaching. Opposing counsel objects to the admissibility of these documents on the grounds that they constitute hearsay. Will the documents be entered into evidence? If not, would you really be required to produce the purveyor?