Small is a pretty subjective word. In the world of beverage packing small might still seem pretty big. Most plants that are set up for hot fill are designed to run 100's of bottles per minute. For example the last tea project we helped with ran about 300 bottles per minute. Speed (throughput) equals cost. The faster a plant goes the lower your price of co-packing. There are small lines out there but because the throuput is relatively low the cost can be quite high. Recently, we designed and installed a small four head filler. This line runs about 4,000 bottles an hour and given the setup time and cleanup time it doesn't really save money unless its used for about 4 hours. So I think the answer to your question is what is your target co-packing fee and how many bottles equals a production run? If your run is under a few thousand bottles it may be difficult to find a plant at both your target cost as well as the appropriate certificates and infrastructure to handle your run - often it makes sense to self-fill until your business scales to a plant's minimum order quantity (MOQ).
I know of a relatively small hot-fill co-packer in New England that is affordable - price based on volume. Let me know if we can be if any further assistance.