Well, it’s really up to you. Bring as much as you want to spend in Uzbekistan. The country is not much expensive but most for paying most of the things you will need cash. Cards are not much accepted here. You can exchange your money at the airport or in any hotel or banks of Uzbekistan (both in private & govt. bank). Keep in mind that you need to pay tips in restaurants and to porters (not mandatory, but expected as it’s almost a custom to tip).