$1,300 isn't bad, and your idea to use an external SSD to be your boot drive is a good one, as well.
Keep in mind that an external booter (I would consider USB3 to be the preferred "way to go", best bang for the buck) will not be as fast as would be an internally-mounted PCI-e flash SSD.
Nevertheless, the speeds would be "good enough" -- you'll probably get reads in the neighborhood of 430mbps.
I called the local repair shop and they said that the temp sensor Cable no longer works on the newest Imac %K and ju have to adjust fan speed with software?
I called the local repair shop and they said that the temp sensor Cable no longer works on the newest Imac %K and ju have to adjust fan speed with software?