You can find the most up to date price for Dash at Coinmarketcap.com or Coinbase. Both will list the price as well as other info like market cap, trading volume and the supply in circulation.
You can also see the Dash price directly from your crypto wallet such as Coinbase and Binance before you buy. Actually all transparent wallets and payment gateways like Moonpay should list the exchange price before you complete the transaction.