Even after your cycle is complete, it is highly recommended that you test the water weekly as ammonia etc can appear long time after the cycle has been completed.
How much did you spend on the tank/ornaments/gravel/filter/heater/etc? My guess is that it was a fair bit more than $40. If you're willing to spend whatever you spent to set it all up then surely you're willing to spend an extra $40 to ensure the wellbeing of the fish which haven't asked to be put into an uncycled tank where their wellbeing will not be monitored.
I'm not having a go at you - mistakes are often made when we start out and we have all been there. I'm just saying: is it really fair that the fish should suffer, and live in the equivalent of a septic tank, as long as they do live and aren't killed by ammonia poisoning etc because you don't really want to spend $40 to buy a test kit.
I'm guessing by your questions that you are new to fishkeeping, like I said, though obviously I could be wrong. In that case I'll give you a bit more information about cycling and the after effects:
There is no time limit for a cycle, it can take as little as a week or two, or as much as a number of months.
Any fish present during cycling are likely to be subject to permanent, irreversible damage that is not usually immediately noticeable, so you do have to worry about levels, long before a fish appears stressed. Nitrate poisoning is possibly most true of this as it can cause liver problems, just as one example, which would take a long time to show up on the fish.
After cycling, it does not mean that ammonia, nitrite and nitrate will remain at 0, 0, < 40ppm. They can each go up at any point which is why it's important to test the water on a regular basis.
The test kit will last you a very long time so it's $40 spread over this long time.
Good luck with your tank.