That said I never had complaints regarding the quality of the results on my custom engine using google API, only that the query limits make it impractical for my purpose. Do you have a suggestion for search API, other than bing with no query limits?
BTW: Google's results using the REST API (free quota) seem to vary with usage. When there's some load, there will be only a limited set of result on the next "page".
Edit: As free quotas are very limited with the new APIs (10/day), I'ld guess the days for any experiments with search operations are over. (If a project gains some interest, you are due for 1M hits/day, and the fees for this are more than anyone would afford for a pet project.) You could try to make a deal with the vendor in question before, but this would result in an amount of planning that is out of scope for a project, which is essentially shoot-and-go.