Pay with discounted ebay gift cards for further savings, but weigh up the cons of this as you have more recourse for faulty items when using the protection when using credit cards and this may come in handy with Dell as they are rated very poorly across review sites.
Some deals:
Dell 27 4K UHD USB-C Monitor - S2722QC 3840 x 2160 at 60 Hz 2xHDMI, USB-C $421.85
Dell 32 USB-C Gaming Monitor - G3223D NVIDIA G-SYNC QHD 165 Hz $551.40