You had better drive the Mirage before signing on the dotted line. The Mirage is a miserable driving, slow, noisy, tinny, and uncomfortable POS. In Consumer reports testing it scored only 29, lower than any car that they have tested since the Yugo. Also, forget the Spark since it is manufactured by Daewoo, none of the cars they ever manufactured were any good, and the cars produced by them brought down Suzuki. Neither the Mirage or the Spark have enviable reliability records. The Mitsubishi salesmen push the warranty hard (how else are they going to sell the miserable Mirage), but keep this in mind, the best warranty is the one you don't have to use.
In that size category you would be FAR better off with a Yaris, Fit, Versa, Rio, or Accent. I know that they are more money, but they are well worth the extra money. That additional money will come back to you during the time that you own it, and you will certainly get it back at resale/trade-in time (especially the Fit and Yaris). If you can't afford a new one, buy a 1 or 2 year old used one.