There are models as cheap as $30. For software check out OpenOCD, some has already taught it about Xtensa processors.
You can emulate JTAG in software but it is slow. You don't want to spend ten minutes waiting on the JTAG when a $50 hardware one would respond in seconds.
I doubt the OpenOCD Xtensa support is as complete as the one of xt-ocd.
And don't underestimate the speed of toggling GPIOs via /dev/mem.
If you still got a PC with parallel port, you can easily build a Wiggler compatible JTAG adapter.
In theory it should be possible to emulate a Catapult EJ-1 with the Raspberry Pi model B.
The Raspberry Pi model A (not B) might be able to emulate the USB JTAG adapters.
Of course one would have to reverse engineer the device's Ethernet/USB protocol first.