If your budget is really only a grand, that limits your choices.

For building a GPU based rig, normally you'd  need to spend about $400 - $500 on the PC hardware (MB, HD, Ram, Power Supply, CPU) before buying the video cards (up to 6 of them on an average system).  each card is going to be about $250 - $700 depending on what you go with.


For a grand theres a couple choices;   buy a used gaming pc from a couple years back if you can find one for a couple hundred bucks and just add GPUs to it.  might start with 2 decent ones, then make some money off of them to build a better / more complete rig later.

The other option is to buy an older generation ASIC miner like the S7 which you might be able to get for 6 - 800 and would be plug-and-play but will only work on BTC.

If you want to actually make money, it might be better to invest the 1k into trading currencies for a few months and see if youre able to make enough to build a more complete solution.   That will also let you learn the different currencies, and learn the process for transacting with the various coins and wallets.