If you don't have tix yet here's your chance to avoid the ticket broker/scalper. The Astros just released more tickets for each of the three home games. I only found singles for Sat., but pairs are still available for Sun. and Mon.
On Astros.com scroll down to "Astros promos"...within that section there is a heading "Postseason Ticket Information"...click that and it'll take you to the Astros Ticketmaster page where you can order on-line.