I say you hire Heather to do the website for the $500, if she needs help she will get Matt to help her and you will have a $1,000 website.
You get a quality website that you know is done right and for 1/2 the price.

You also help out Heather and Matt.
If you do go with the other guy I would pay Heather or Matt a small fee to tell you what to look for and what to make sure you get in the deal with this guy so you do not do $500 worth of labor and engineering on the deck and get a $100 website. Not to mention the wear and tear on your tools. I am guessing he may not need you but really needs your tools to get his deck built. But Heather or Matt can talk to you about what they would charge you, they may even be willing to apply any consultant fee or portion of to the cost of the website design. If you feel they would be a better way to go.
Heather / Matt Sorry if I am over stepping my bounds here.