To add to Michael Bloch's important points regarding purchasing t'fillin from a reliable seller and borrowing t'fillin for use in the meanwhile:
I'd advise you to CYLOR, but it seems from the Mishna B'rura (32:172) and his extended discussion in Bei'ur Halacha on 32:38 (s.v.v. "יעשה" and "מעור אחד") that one can rely on the lenient opinions regarding p'shutim if necessary.
It is probably not advisable to wait if this means not wearing t'fillin at all in the meanwhile. The Talmud (Rosh HaShana 17a) categorizes people who avoid wearing t'fillin as "Jews who sin with their bodies,"1 and the Bach (OC 37) interprets this stringently as even including people who have nothing against wearing t'fillin but miss wearing them because they are busy with other activities or with work.
Perhaps the Bach would not apply this category to people who temporarily miss wearing t'fillin in order to save up money to eventually fulfill the mitzva in a better manner. However, due to the principle of chaviva mitzva b'sha'ata ("a mitzva is most dear when performed in its proper time," P'sachim 68b), it may very well be better to wear inferior t'fillin now than to continually miss the mitzva until you finally obtain a superior pair.
There is a lot more to be said on each of these points, and there are various opinions regarding just about all of the aforementioned. In the spirit of this topic, however, I figured I would post a bare-bones answer now, rather than not posting anything until later.
1 See the P'ri M'gadim (Eshel Avraham 37:1) who cites the strict opinion of the Nachalas Tz'vi that this even refers so someone who misses wearing t'fillin for one day: "עיין מ"א אבל בעטרת צבי ס"ק ב ונחלת צבי ס"ק א פירש דברי השו"ע כמו שכתב בב"י ד"ה וכל דאפילו אין מניחן מאיזה טעם שיהיה הוה בכלל פושעי ישאל בגופן ועיין ב"ח ד"ה גדולה מלת בכלל ואפילו יום א' שמבטל ולא הניח הוה בכלל פושעי ישראל כמו שכתב בנחלת צבי שם יע"ש".