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 hours. They felt that providing an easy to understand pricing is a sign of respect for the customer and decided to only 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. For GPU based rendering, they use quad Nvidia T4 GPUs, (16 GB RAM) or better servers.