BlenderRenders used to have one of the best prices for online blender rendering. The pricing is comparable with what RenderStreet, the company that acquired BlenderRenders, has.
RenderStreet has a single pricing model, by server hour for the on-demand plan. They felt that providing easy-to-understand pricing was a sign of respect for the customer and decided only to use such a price. Their price varies between $3 and $4.49 (for CPU and respectively GPU servers), depending on the membership level you get with them. There is also a fixed-fee, unlimited rendering option available with the RenderStreet One program.
The servers RenderStreet uses are very fast. For CPU based rendering, they use dual Xeon servers, for a total of 32 to 56 render threads. They use quad Nvidia T4 GPUs (16 GB RAM) or better servers for GPU-based rendering.