you might also find that keeping your "leed eye" the one you site with directly over the blade and cutting line will help.
if you watch the cutting process and the line you are following from a side aspect, you will tend to push away from that line and then re compensate for your deviation by pulling back on the saw, the blade will flex and you'll end up with that obtuse angle of cut that you are finding you have.
i have both cheep and very expensive jig saws, and like any cut you make, be it with a craft knife, chisel or a saw, power or hand, unless your siting eye is directly over the cutting blade, you'll ALWAYS end up with an angled cut.
don't change your saw, just change your cutting technique.
neil.