First of all, I don’t own any franchise or gas station – so take my advice with grain of salt.
My input is strictly based on anecdotal evidences and stories.
Minimum investment required for a gas station, obviously, depends upon location and size of the unit. Most of the time when you buy a gas station, you are only buying a lease for the station for certain number of years (I’ve heard 10-30 years). Many times these deals are done in cash, but sometimes financing is used as well. I’ve heard investors putting in any amount from $50K to $300k for a 25% stake to 100% stake in the venture. Then you have to deal with cost of repair, maintenance and finally operation of the station – so have some money aside for that as well. You have to plan also on how you will address any lawsuit (from private party or EPA) if they come up. What I have seen is if you turn a small run-down station to a clean mart, there’s some profit to be made as long as it is in a good location. You don’t get much profit from gasoline itself, it’s the other stuff you sell in the mart that brings the mullah.
Let’s get to your question about franchise or own startup. If there was one answer, don’t you think everybody would be doing the same thing? Franchise comes with heavy upfront price tag just for licensing as well as setting up the business – but also comes with valuable support system that is essential for a newbie. Do research on which franchise makes sense. Some can be started for reasonable amount like $30k, others require much more. Many Nepalis own multiple 7-11 and Subway franchise. Look for others, there was one bloke who strike it rich by opening a franchise for gutter cleaning.
As for a startup, that’s such a broad topic, Are you talking about IT startup or merchandise? They all have their own plus and minus.
Bottom line, do a lot more research before you get into a business. Just this forum won’t be enough. More importantly, expect to be involved with your business 100%, 24-7, specially for first few years.
Good luck, hope this helps.