If it's a 7 speed hub, isn't it going to be a 126 mm rear triangle? If it's aluminum and 126 mm, it's not really made for a 130 mm hub, which is the OLD for 8+ speed hubs.
Perhaps a better approach might be to ride, save some money, and buy a lightly used bike from your equivalent of Craigslist. Some riders upgrade frequently and essentially give their old bikes away. Others buy a nice bike, find they don;t like riding and then sell their bikes.