Have you let the hose run for hours to soften the soil to make it easier to dig? It makes a world of difference.

If it's really THAT hard, you could use a jackhammer to break the ground up, and a shovel to scoop it out.

If you can't do it yourself then it is not DIY is it? You should have someone look at the job and make a bid so that you can make an informed decision between injuring yourself or your bank balance. If you need to excavate you also need somewhere to put what you excavate and some means of getting it there, then you need to get the fill material into the excavated area and so on. These steps all require physical labour as well as the appropriate tools.

Look into renting a TORO Dingo or Bobcat MT-52. You'll need a couple hours to get used to it if you've never used a mini skid-steeror full-size version. Make sure to get a toothed bucket.

The same rental place will have plate compactors which are necesary to install paver properly.

If the ground is that hard and devoid of organic matter you may only need to dig a little deeper than the thickness of the paver and enough sand to level it.