I have looked into the franchise advertisements for places like Subway in the past.
Here you go: http://www.subway.com/subwayroot/own_a_franchise/FranchiseFAQs.aspx
That is the legit Subway company's website and Frequently Asked Questions for those interested in a franchise. It kind of gives a picture of the cost and such. Realistically, it can be a minimum of anywhere from $50,000 to $100,000 that you have to have money-wise in order to be able to start out. Are you SURE your parents would help with that?
Note that a lot of these "franchise owners" make a decent living. They might make around $50K to possibly even $80K-$100K a year if they are really successful. But they also don't have a lot of time away from work. They might work 60+ hours per week. It is a very taxing job.
According to that site, the initial franchise *fee* alone and by itself is $15,000. That's just a fee and not related to the establishment itself. From the website: "With location flexibility and an easy-to-run operation built on simplicity and efficiency, our start-up costs are lower than most restaurants. The initial franchise fee is $15,000, and total investment can be as low as $78,600. Individual costs vary, so contact us for more details."
If you're in the USA or Canada, take a look at this: http://www.subway.com/subwayroot/own_a_franchise/PDFs/Capital_Req_US_Canada.pdf
It gives an estimate of the lowest cost and highest cost potential. For everything, it can range from $115,000 to $258,000 on the high end. It mentions on the site that they (Subway) have various banks and financial institutions that can give you loans. However, look at that charge in the last link. A lot of that money they want up-front in a "lump sum" for most of the fees. Most people with even 4 or 5 people cosigning on a loan together wouldn't get approved for such a massive loan, especially nowadays.
I wish you well, but I hope your parents are really financially blessed or something. Nothing is wrong with your ideas or ambitions. Just research to see what you'd be getting yourself into. Then there are ongoing operating costs WHILE you are paying your loan back to the financial institution. At $100K to $200+K loans, that's a LOT of interest.