I am about to launch a beta site, and heroku looks like a great option. The only think that is getting me down is that the only search option is $20/mth for the Websolr
IndexTank has a heroku addon you can use for free.
It has some advantages over websolr, like realtimeness, fast (all in ram), and a very flexible scoring system that doesn't require to reindex (allows for very easy a/b testing).
If you're using Postgres for your Rails app then take a look at this free way to do full text search:
Part 1 and Part 2
This uses the pg_search
gem to allow you to use PostgreSQL's pg_search_scopes
feature and have full text search without any other dependencies.