As a small thing, the site returns a server error if you enter >=$1350. It may be that there are very few people searching in that range, and you're not really worried about it. If it were me, I'd link to your most expensive build (the one for $1350) and then give a small message suggesting where extra money can be spend (SLI, crazy case, more HDD, RAM disk, etc.)
Edit: Now that I see the 'improve' and 'cheaper' buttons, and that they let you exceed $1340 if you manually 'improve' components, I'd be more concerned about the server error. Also, to make the 'improve' and 'cheaper' buttons more obvious, I'd put a prominent banner right above the build you return, where you point that function out to the user.
Edit: Now that I see the 'improve' and 'cheaper' buttons, and that they let you exceed $1340 if you manually 'improve' components, I'd be more concerned about the server error. Also, to make the 'improve' and 'cheaper' buttons more obvious, I'd put a prominent banner right above the build you return, where you point that function out to the user.