A simple 10g kit with low-PAR light, simple heater, and low-power filter might cost $30 at your LFS. This can be placed on a kitchen counter (mine is), a dresser (another one), a nightstand, coffee table, etc. $30 can easily be the cost of a batch of fish. My personal experience with my local national chain LFS is about a 50-75% survival rate. Generally, either almost all survive, or none, plus much of the pre-existing fauna.
This is a no-brainer. There's a significant potential that everything you buy, and then some, will kick the bucket. Keep it in a QT, and you can recoup most or all of your investment. Add it straight to an existing ecosystem and you might lose everything.
This is an expensive hobby. Fail to quarantine and your losses can easily be exponential. Honestly, it's not worth a discussion, IMO.