Append custom field text to title

New to this web development stuff...I have a simple post submitting form in my site. In the post title, I would like to add a custom field (a price) to the title when the blog post is created. The price field is defined in the form as well. Any ideas how I could do this?

Example....

Title: Some blog post title
Price: $3.49

Actual blog post title: Some blog post title - $3.49

thanks for any help!