It's worth mentioning that at the time of writing, the RTX 3070 is still a few weeks away from release, and it's probably going to sell out quite fast. If you absolutely, positively have to build something now, you could go with the older Nvidia GeForce RTX 2080 series, which is currently dropping in price, or the similarly powerful AMD Radeon RX 5700 XT. However, AMD will also release a new GPU (the Big Navi) shortly, so it's probably best to just be patient and catch a restock.