You and hordes of others are trying to do the same thing thanks to an unprecedented altcoin rally which is resulting in huge profitability (currently) for anyone mining altcoins on GPUs. This has caused a run on the GPU market and supply is unable to keep up.
The supply is so constrained that even used GPUs are being sold at up to 30% or more than the suggested retail price of the same item's price listed when it was brand new.
The rally was so intense that even at those GPU prices it is still fairly profitable to mine, and possibly the opportunity will continue. This is because hashrate lags price, and the lag for response to this rally will be prolonged because there simply aren't many GPUs available in the supply chain even, at this time. Stock available from the manufacturers takes months to reach retailers when the route includes transport by ship, for example.
The most profitable time to mine is before difficulty rises, so waiting for GPUs to return to stock will likely coincide with lower profitability.
So you have a few options, including the one where you bite the bullet and pay for the overpriced used units. Many retailer chains have inventory shown online, so you can check if they have any store locations near you with a decent GPU in stock. Some retailers might have a display/demo unit not included in their inventory count that they will sell (especially if the unit is an outdated series, like the AMD 480s now are.) You might even find a couple hours drive to another city might yield you the GPU you can't find locally. Also check Craigslist, as there might be some seller not realizing their "gaming" PC actually makes a decent mining PC.
If your problem with the AMD 580 you tried is simply related to the geth client, and your aim is to simply acquire Ether ($ETH) cheaply, you can mine many other GPU coins at near the same level of profitability and trade the proceeds for $ETH.