Deal: Grab the dual-SIM, unlocked Samsung Galaxy S10, S10+ and S10e for 20% off
However, if don't meet the requirements that would allow you to get a cheaper Galaxy S10 phone from Samsung, or don't want to commit to a long-term contract with any of the US carriers, your best bet is eBay, where you can find the unlocked models for low prices.
For example, eBay seller never-msrp is now selling the Galaxy S10e, Galaxy S10, and Galaxy S10+ for around 20% off. If you don't mind owning the international models that come with Samsung's Exynos 9820 chipset inside, which proved to be slightly less powerful than the US versions that pack Qualcomm's Snapdragon 855 processor, then here is how much you'll have to pay for them:
Keep in mind that since these are international models, they will only work with GSM carriers like AT&T and T-Mobile. The good news though is that you can take advantage of the secondary SIM tray that the US variant lacks.