If they build the League around existing RL areas, they'll keep travelling costs down until there's more money in the sport.
They may miss out on 'big name' cities, but that would be better than parachuting in a ready-made franchise and watching it wither.
You have it backwards, there's no possibility of starting a sustainable pro league in the US without bringing enough money into the game first. If it's going to work it needs to be done the American way.
For the league to get off the ground it first needs what the American Football League had when it started in 1960: a TV partner willing to pay for broadcast rights and enough investors with the money and interest needed to buy franchises. That's how the pro sports business (and it is a business) works in this part of the world so that's what's needed to make a go of the venture.
How much money do investors need to have? What I've read about the business model of pro sports says that it takes at least 5 years for a new league to reach the break-even point and therefore franchise holders need a net worth that's at least sufficient to underwrite the first five years' operating costs for a franchise, maybe more in this case since RL's a sport Americans don't know at this point. Daunting though that sounds, there are hundreds (if not thousands) of well-off Americans who would love to get into the pro sports business, football most of all.
RL can be viewed as an international brand of football in our sense of the word, "the other football" as some in Jacksonville have apparently called it. That means the proposed US pro league would be a ground-floor opportunity for the people who'd love to own a football team but can't otherwise because NFL teams cost way too much and unlike baseball and hockey there are no minor pro leagues they might invest in. If they like the league's prospectus and the business model it outlines, RL could be a great option for them. The franchisees can then work out how best to appeal to people in their local markets.
Travel costs can be kept lower in the standard North American fashion of having geographic divisions with an unbalanced schedule. If it has a spring/summer schedule and playoffs like the USFL did when it was operating, this format could work well. Ten teams in two 5-team divisions would be good, 12 teams in two 6-team ones would be better still since it would allow for a better playoff structure.