The pay for these recruits is the same as any other soldier of the same rank and time in service. It's not based on their high school completion status. Pay is determined by rank, time in service, and any special pay entitlements. You can find current pay charts on the official Department of Defense or Army websites.
Crucially: While they can enlist, they are typically *required* to complete their high school education (GED or equivalent) while serving. Failure to do so could lead to consequences. Therefore, while the *initial* pay is standard, the long-term pay and career advancement opportunities depend on completing that education.