You are looking at bike in the $150 price range. To convert them in a way that isn't completely ugly will likely cost at least another $50. You could instead buy this or a bikes direct bike or a nashbar cheapo and have a bike with the proper dropouts etc. You should really only convert a bike if you like the bike and want to convert it. Conversions do not end up being the cheapest way to go any more and only make sense if there is something about the frame that appeals to you.