Quick summary answer: You must promote this using direct mail to businesses who are in the right geographic region to take advantage.

Buy or rent lists from: Chamber of commerce, local business association, local council rates payers etc. Also find organizations that have mailing lists and agree a deal with them to promote to their list.

Get each to send a direct response email that drives readers to your landing page which includes these 3 things
1 - re-iterate the offer
2 - give a guarantee of quality
3 - add testimonials

Have an on-page registration form to allow you to phone and qualify each enquiry.

As an additional benefit you could get firms to refer others to you for an extra discount if their contacts sign up.

Note you'll need a strong process for follow through to ensure nobody gets overlooked.

Go gettem!

This is an awesome promotion and really appropriate for SMEs I'm so glad you have gotten great support.
If you need help writing the landing page, or introduction email, please get in touch.

What's the catch? I'm in touch with literally hundreds of people who'd agree to a free website in a heartbeat, including me.

Thousands of easily identifiable people need sites built. I trip over them daily. The challenge is getting people to pay for your work.

I would suggest advertising on your site and elsewhere a limited time offer that you can get up to $5000 off a website. Then simply explain once people start inquiring that it is a money back grant on the site. Don't compete with words like grant or free but instead get the word out using word of mouth and relevant dispersal in communities revolving around website design.

1) Identify a list of 20 local businesses who have horrible websites.
2) Reach out to them via email or social media.
3) Send them your portfolio and reference the grant.
4) Line up coffee to chat with them about how it could work for them.