I have found that Melodyne yields very realistic harmonies. Vocals are monophonic so the Melodyne Essentials would do the job perfectly, i.e. about $99 USD.

Waves is a very reputable company and in fact I own many Waves' products. The harmony examples do sound very good however based on only that I would pick Melodyne. YMMV

Here is a list of some free ones so maybe one of these would work for you:

https://midination.com/vst/free-vst-plugins/free-harmonizer-vst/

I have no experience with any of these.

Google/Bing harmony vst and I'm sure that you will find something that will work for you and is in your budget.

I hope this helps and good luck.


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