Can my portal show prices in my customer's own currency instead of only one?

Yes, in most cases a portal can show prices in more than one currency, although how many you can offer depends on your suppliers and on your payment setup.

The way it normally works is that your suppliers quote fares and room rates in their own currency, and your portal converts that into whatever currency the customer is viewing. The conversion can run off a rate you set yourself or a rate that refreshes automatically each day, and you can usually add a small buffer on top so a movement in the market during the day does not eat into your margin. Many portals also guess the right currency from where the visitor is browsing from, with a selector so the customer can switch it if the guess is wrong.

The part worth separating in your mind is the currency the customer sees and the currency they are actually charged. Those are only the same if your payment provider can settle in that currency, and some providers handle only a limited set. Where they cannot, the customer's own bank does the conversion and the amount on their statement can come out slightly different from the amount they saw on screen, which is worth saying plainly on your checkout page. There are also cases where a supplier quotes in one fixed currency only, or where an air ticket has to be issued in the currency of your point of sale, so you cannot always sell in anything you like.

A good next step is to check which currencies your suppliers quote in and which ones your payment provider can settle, then decide your display list and your conversion buffer before you go live.