Secondhand is fine, to an extent.
When you're getting faster (ie 3rd gear) the risk of bigger damage goes up so you want consistency so it's best to run new. Keep an eye open for cheap new tyres in sizes that suit. We tend to get 215/45/17 for around nzd$65/tyre (£30/tyre) and they last twice as long, so if you can spring extra coin at the time it's worth it.
Look for tyres with high treadwear (400+) and ask around what people use. Most will remember the good, and definitely remember the bad
Keeping an eye on tyre pressures after each run and dropping them back down to what you start at drastically lengthens tyre life, secondhand or new