The delay is not the end of the world. You will notice it if you compare them side by side with a flasher, but it's something you get used to fast. I have a Helix 8 that only gets used on the boat. My fishing buddy runs a Helix 7 ice fishing combo. The GPS maps is the best part of them. Mine has side imaging, which is fun in the summer. You can buy 360 transducers to use that feature through the ice. I'm not a fan of the Helix 7 for ice fishing, but my friend loves his. I am too hard on things to bring my helix out, they are delicate. They are also crazy expensive. The map chips are too expensive. I wouldn't buy my helix 8 again, knowing what I know now. I use a Vexilar FLX-20 ice fishing. One of the main differences between us is I am almost always outside, I don't use a shack often. The Vexilar is way easier to see in full sun.
You aren't going to touch a Helix 7 under $500, more like $800-$1000 unless you find a used one. Map chips are another $150-$200. The only flasher you list that meets your stated $500 limit is a Vexilar FLX-20, and they are great units.