I had a couple of plants that were contaminated with spidermites and since money is tight I was wondering if it'd be okay to re-use the same soil for other plants without the risk of having another outbreak?

Hello your highness

Personally i wouldn´t do it. Also old soil often has problems with water absorbtion and it can be
difficult to give your plants the right amount of nutrients.
You could probably get rid of the spidermites but i don´t think it is worth it.

Hope this helps

Have a gud one

This will eliminate most if not all pest problems.

step one : buy cold pressed neem oil.
Step two: Mix the appropriate ammount of neem oil with water.
Step three: water soil thoroughly and let dry.
Step four: After soil is completely bone dry I mix a cup of food grade diatomaceous earth into the soil.

As SIB said, the Neem will help to make sure that the mites do not come back. But, that being said, there are no guarantees. You will want to continue to use the Neem. The DE, in my experiences will only work while it is dry, so as soon as you water it the first time, it's effectiveness dwindles. You may need to use something stronger if the Neem does not work 100%.

That being said, all of my pots have been re-used and we have a pretty significant aphid presence in our area. It is all about keeping up with the deterrents. As long as you treat the plants regularly they will be fine. Just make sure that you stop using whatever it is a few weeks before you harvest anything, and wash any leaves before ingestion

Hope this helps. Have a blessed day.

you could bake the soil as well.

Look into organic preventative measures such as nicotine sprays.
I reuse old soil after composting it for a year and believe me it gets infested.
make sure to follow shamanisticvibes advice on the DE though that stuff needs to be kept dry to be effective.