Cryptomining with a "cheap" server.
If you look online (ebay) you can get HP servers for under $600. If you get a good one with fast Xeon Cpu's (E5645 or greater) you get +300 h/s on Monero and/or Bytecoin before even adding a video card. Bonus is they come with plenty of ram and reasonable hard drive space. My server I bought HP Proliant DL380 G7 for $500 has 4 SAS hard drives (450 gigs space total, with room to add 12 more if I wish)) in raid 5 with 128 GIGS of ram! and 5 gigabyte Nic's. I added a riser card for PCIe x16 (additional 80 bucks off ebay) so I can add a current video card (Friend got me an RX 480 to split the mining profits) into the server. Total hashrates will be about 1400 h/s and the bonus is a server that I can use to store and share files in the household.