Hello, please read everything carefully before answering. Thank you!

Last year when I turned 25, I decided to purchase a bicycle after a Huffy Panama Jack caught my eye. I had not rode in almost a decade, but quickly fell in love with cycling, and it now it has become a passion. My dilemma, a cruiser is clearly NOT meant for speed or commuting. It is time to graduate to a better bike..

-I am 5 foot 7 inches, with a leg length of close to 31 inches, a 29 inch waist, about 148lbs.

-I use my bike to commute to work, 14 miles round trip about 3-5 days a week, which is mixed terrains, mostly in the street and on sidewalks. I also use my bike to cruise around Metro and State Parks, but I don't do major off-roading, most of the bike trails at my local parks are paved.

-I travel long distances, and would enjoy riding for several hours a day, but on my work commute I see mixed terrain such as curbs, sidewalk cracks, small pot holes, debris such as pebbles etc. But for the most part, I am riding on pavement.

I have read that I should fit most properly on a 17.5in or 45cm Mountain Bike frame, or 21in Street Bike. But I am undecided on which I should purchase, and not positive if this information is correct.
I have also entertained the idea of a Hybrid bike, which apparently has tires suited more for the road, but the comfort of an upright position, which would be great because I sometimes get lower back pains.

Also, if anyone can suggest a decent inexpensive starter bike in the $170-$300 range, it would be much appreciated. And before I get slammed with criticism of "unrealistic pricing expectations", take note that I am not entering into races or going cross country, and I rode my $140 beach cruiser 14 miles round trip to work and back like it was going out of style, so I am really just looking for something more practical and better fitting, not necessarily top of the line.

Thank you very much for the help!
-Jeramie
@ Old Hippie. You managed to answer one of several questions, other than that you just made sarcastic remarks. This is Yahoo! *Answers*, not Yahoo! Personal Opinions.

To answer your question, there are small segments of my commute where I must cross a sidewalk briefly, or briefly ride through a parking lot.

In response to your last statement, I specifically stated "And before I get slammed with criticism of "unrealistic pricing expectations", take note that I am not entering into races or going cross country, and I rode my $140 beach cruiser 14 miles round trip to work and back like it was going out of style, so I am really just looking for something more practical and better fitting, not necessarily top of the line." I am clearly not looking for something that is going to last a decade. I am just starting out.

Don't be a snob, while they may no be the best bikes, there are Mountain Bikes, Road Bikes, and Hybrids in the $170-$300 range that are better than