The Mariners have had a very busy offseason (something that Mariners fans have come to know well with Dipoto leading the ship). This roster has undergone a massive change with a new starter in five of the nine offensive positions (DH included). They have done this via free agency as well as trade and they have built quite a solid roster, all while they have been under a pretty strict financial budget. Dipoto and Hollander have done a great job addressing their biggest needs at both corner outfield positions, as well as second base.
This team, as it stands, would be a solid team heading into spring training where they can get a look at a few different people to see if anyone sticks out and forces their way on to the roster. The Mariners' payroll currently sits around $123 million, if you figure their budget is what it was last year, in that $140-$145 range, they still have quite a bit of flexibility.
You figure they want to keep a decent portion in case of any midseason trades, but let's say that's $10 million, which still leaves at least $7 million and possibly $12 million (both of the following options could be had for less than those amounts). If the Mariners really want to win this offseason, however, and make themselves the division favorite, they will be aggressive and try and sign one of the following outfielders.