Hostgator provides support to both Ruby-on-rails and PHP. But looks like PHP may have a upper hand with wide user base and plenty of online resources.

Mustard Seed Requirement
1. Sales person can update buyer info into a form.
2. Contract is automatically generated with info collected from form

Good to Have Requirement
1. Sign directly on form
2. Mail signed form to buyer
3. Store information in Database. Drawing down the available houses in stock.

Below are several tools/extension that we can look at.
1. TCPDF – FLOSS PHP class for generating PDF documents.
2. http://coding.smashingmagazine.com/2009/01/20/50-extremely-useful-php-tools/
3. http://phpexcel.codeplex.com/
4. http://code.ohloh.net/ – Free code search engine