jeremyshoning
Along with what maratsade suggests, which is printing the Billing Detail Information, which will show the last invoice number and the current balance (which would be zero if paid), you can also print the Account History, which will show the invoice number, the date it was generated and the date it was paid. It's not a payment receipt, but it will show the payment dates and the methods of payment.
You can find the Billing Detail Information, and the Account History (underneath the Billing Detail Information), under both the Account Information and My Bill headers of the HughesNet MyAccount site.
If you need to print a copy of the invoice itself, as in similar to what would be mailed to you if you were on Invoice Billing, you can click on either the Current Invoice or one of the past invoices in Invoice History. There will be a Print button when viewing the particular invoice. The older invoices are on the My Bill page.