I simply order the 1000 envelopes from Quill and run them thru the printer.  I have envelope and database that transferred names and addresses from last year, so return and taxpayer address prints right on envelope.  Thus I don't use any labels or need someone to send pre-printed envelopes.  Cost is only about 6.5 cents per envelope or $65.  And that is free shipping over $50.  Toner cost should be minimal I would guess.