The best way to combat bot spam on a specific form on your website is to add a Google reCAPTCHA at the bottom of the form. If you're not familiar with Google reCAPTCHA, it requires each user to prove they are human before submitting the form and it looks like this:
For more information on how reCAPTCHA's work, please visit Google's reCAPTCHA website.
For most forms, it takes us 30 minutes of programming time to add a Google reCAPTCHA to one form, which is billable for $87.50. This is not the case for every form, please contact us for an estimate tailored to your website.