Our GX430t with WiFi works great. Bought on ebay for under $500. You should be able to get a direct model with WiFi built in for less, but in any case the transfer model also prints direct. I agree. I would not use an external dongle. Built-in is the way to go.
The caveat is that we use it for thermal transfer barcode sticker printing, not Shipstation printing. I'd be very surprised if it did not work though.
Shipstation does not officially support networked printers, but we also have a GK420D which is connectd by ethernet and Shipstation Connect prints to it just fine from a wirless workstation. So think about whether you really need the printer itself to be wireless, or whether you can connect it to a nearby workstation that can act as a wireless print server.
FWIW I think 203dpi is fine for direct thermal shipping labels, and there is usually a speed disadvantage to using 300dpi if you don't need it.
