だけましだ is a set phrase indicating that ‘at least (A)’, or that ‘one should feel grateful for (A)’. This expression is often used in cases where the overall situation is negative, but it is still better than the alternative. This structure is a combination of the particle だけ ‘only’, and the な-Adjective 増（ま）し, meaning ‘better’, or ‘preferable’. Originally, まし is just the conjunctive form of 増（ま）す, an う-Verb meaning to grow or increase (like 増（ふ）える). Due to this, the literal meaning is ‘even just (A) is a plus, compared to what could have occured’.
だけましだ will be used primarily after verbs, い-Adjectives, or な-Adjectives followed by な.

• 天気（てんき）はあまり良（よ）くないが、久（ひさ）しぶりに旅行（りょこう）に来（こ）れただけましだ。
  Although the weather isn’t the best, I should be grateful that I am able to travel for the first time in a long time.
• このアパートはボロボロだけど、職場（しょくば）に近（ちかづ）いだけましだ。
  This apartment is a wreck, but at least it is close to my work place.
• 味覚（みかく）はないかもしれないが、元気（げんき）なだけましだ。
  Although I can’t taste, at least I am feeling well.

In the vast majority of cases, まし will simply be written in hiragana, or even katakana as マシ. The katakana version often further emphasizes that one should be grateful for (A).