If money is that tight I would commuterize what you have now. Slicks would be my first choice to change over (I have Specialized Fatboys 26*1.25 100psi) which I have on my hardtail. A rear rack and fenders would be my next purchase since it sounds like you want to make it more utilitarian. Lights and reflective gear is also very useful.

For relatively short distances (3-5 miles for me) my hardtail is fine. For distances over that I would need to make changes to my bike if I want to keep it comfortable. I am not sure if you are facing that problem as well. If so you may need to look into changing your saddle, pedals, grips, and/or handlebars to help. Hope this helps.