First of all, the important thing to note about our infrastructure is that we are primarily on-premise. This drastically lowers our cost (by about 10-15x) -- and we only have to buy servers once, instead of paying cloud instances each month.
Currently, our server rack has 6 server blades. Each blade has a dual-Xeon. A portion of the $10,000 is allocated to amortizing the cost of these servers. If we receive more than $10,000, and therefore have even more users, then we will simply purchase additional servers.
We don't pay for electricity and bandwidth is negligible. These on-premise servers are only used to transmit the Verilog code and run the synthesis-engine. Typical compressed bitstreams are 3 KB.
Bitstream caching also helps to reduce redundant compute. See the below Q&A for more info.