I think,rather it would be much better to Run an adwords campaign with Less number of ,but lot more targeted Keywords.
The More the Keywords are Targeted and also the less in Number,your Quality Score will be very high and hence your CTR will be higher and hence your CPC will be kept Bare Minimum..
If you still look for answer ,Just Check these out:
1.How to Choose your Adwords Keywords Properly?
2.How to Split Test to manage you Google Adwords Campaigns for Effective Conversion?