It is fairly simple. Stock price is to a degree irrelevant by itself.
Ups is priced at $107 per share the important part that goes along with it is there are 688,770,000 shares outstanding for the company. $107 per share times 688,770,000 shares equals roughly a $73.5 billion valuation.
Even though FedEx is $206 per share they only have 267.38 million shares outstanding (much, much less than half the shares of UPS) which equates to a valuation of $55.12 billion.
Complicating matters we could dive into P/E ratios but instead I will go long story short. FedEx has a very slightly higher P/E ration which means the stock price is slightly more expensive than UPS because its stock price Is selling 1.3% higher on their earnings.