The fees on Avalanche are dynamic. Meaning, they fluctuate with the demand of the network and float between 75 nAVAX (gwei) and 225 nAVAX (gwei).
Transaction fees on Avalanche are paid in AVAX. In order to do transactions, you need AVAX. When you bridge over assets, you should swap some of them for AVAX so you can pay transaction fees.