Hey there, guymarshall.
Basically for that budget you should be able to get a 5-6TB drive probably, depending on where you decide to get it from.
Since you don't mind if the drive is internal or external, I'll show you two options (one of each) if you decide to go with a WD drive.
1. Internal - if the drive is going to be used mainly for backups and storage, then I'd recommend the WD Blue drive (the new ones with higher capacities than 1TB). They have all the features of the WD Green drives and that makes them just as cool and quiet while running. You can take a closer look at the WD Blue drive's features here:
WD Blue
2. External - if you'd like to go with an external HDD, the WD Elements Desktop drive should be up to the task. It's a 3.5" drive (externally powered), which comes with capacities of up to 5TB. You can check it out here:
WD Elements Desktop
However, I'd like to make one point clear. Getting a large drive to store your data is not a backup solution. This is basically storage. In order for it to be considered as a backup, everything you store there should be a copy of the data you already have somewhere else (another drive, cloud storage, different computer, etc.) and not just stored on a single drive.
Please let me know if you have any questions.
Boogieman_WD