I would get a hybrid bike unless the non-path is TOO rough and if you never plan on actually doing actual trails. I am on my second month of a Cannondale Quick 5, last year's model, and it cost me $350, which is a really good deal. I use it to commute.
I don't know how many miles you are getting in now but if you need to work up to the full commute here is some suggestions:
- If there are places along the way from home to work that you can park and get to the path try getting within 10 biking miles and going from there. When that is no big deal extend that distance and then keep going to where you can fully commute every other day. Then when you are doing it every other day you can then start back at the 10 mile point for the in between days. Work incrementally so you don't burn out and you become consistent.
- On day 1 take your bike to work in your vehicle and ride home. Then the next morning ride in. Then the next day take the bike in again. That gives you one 20 mile ride a day.
- If you don't have a shower at work try to negotiate a "shower only" membership at a local gym. I did that and it is working out well.