EZ-Link pass is a general transportation card that is being used in Singapore to ride MRT and city buses. Just tap in and out with it as long as there is enough credit.
I’m using the same card whenever I have a layover or a short vacation in Singapore.
To add credit to it without extra fee, just go to any GTMs, short for General Ticketing Machines, in any MRT stations like in Changi Airport. They are mostly located near the top-in-and-out machines.
GTMs are easy to navigate and English menu is available. Both debit or credit card, and cash payments [Singaporean Dollars] are accepted.
The minimum top-up amount as of writing is S$10. Hope this info will help create that budget!
Tip: I bought an EZ-Link Pass the last time from a booth in Changi Airport for S$12.00. The card cost was S$5.00, and the rest was the initial credit.