If you're in Europe, there are a few major EMSPs that provide you access to multiple networks. The two biggest players seem to be New Motion owned by Shell and PlugSurfing owned by Fortum. In most major countries these two have a massive percentage of the chargers and networks. In some they have 100%.
The pricing is down to the CPOs and the same charger can cost different prices based on what deal they made with the EMSP.
Source: I work for a EMSP.