When we are not playing Texas, you will do OK. You can always buy tickets from sellers/scalpers outside the park (even get a deal right at game time).
But if we are playing Texas, bring some extra cash. I shopped hard for some reserves seats in 2007 to see Texas-Texas A&M play the final weekend of the regular season. I was able to get 3 tickets for $110 (3rd base side, shallow outfield).
I do not think any Reserved tickets are available (not online) as season ticket holders have been buying their own seats for regionals since May 5th. But as I said, you can probably get some reserved seats from a scalper.
I would get GA now as a backup.
Brian