Real-Time Currency Exchange Site

I need a straightforward web application that lets visitors calculate foreign-exchange values instantly. The only feature I require is currency conversion, powered by real-time exchange rates pulled from a reliable API.

The site must handle these pairs: USD/THB, USD/KHR, THB/USD, KHR/THB, THB/KHR and KHR/USD. A clean interface showing “You send / You receive” with an auto-refreshing rate display is enough; no user accounts, log-ins or stored transaction history are necessary.

Please deliver:
• A responsive front-end where users pick a pair, enter an amount and see the converted figure immediately.
• Server-side logic that fetches live rates every few minutes (open-source API such as Fixer, ExchangeRate-API, or a solution you propose that covers the listed currencies).
• Clear instructions so I can change the API key or add more pairs later.

Accuracy and speed matter most, so cache calls wisely to avoid rate-limit issues while still feeling live to the user. I’m open to your preferred stack—Laravel, Node, Django, or similar—as long as deployment on a standard VPS is smooth.