Some ETH and USDT Advice

Hi guys, so I need some ETH and USDT advice... I’ve currently got some USDT stuck (approx $600) over on Trust Wallet and with no ETH for gas fees to convert it to any other coin at the moment, however if I buy some ETH to cover the gas fees what are the fees most likely to be and what percentage will it be to the value of the USDT? I don’t want to buy some ETH and then get stuck because I haven’t bought enough, and I don’t want to pay the equivalent to the value of the $600 USDT just to unlock it, which makes no sense right?

I originally bought the USDT on Uphold and sent it to my Trust Wallet and now want it to go back to Uphold where gas fees are almost non existent.. So how do I do this? I have been advised that converting the USDT to something like TRX is by far cheaper option, or converting to DASH and then transferring back to my Uphold where I can convert it back to USDT to save my gas fees, but I don’t know how much ETH gas fees I will need to unlock the USDT? Hope you can shed some light on this.. Thanks ????????????????