Cremation and burial of the ashes in an existing family grave, or scattering of them in the desired cemetary, would be a more cost-effective option: OP should look into that possibility.
More cost-effective is a relative term. My spinster aunt was cremated and interred in the famous Boston Cemetery where her parents are buried. To open their plot to place her already cremated body (Neptune Society, I believe), the fee was $5,000. Yup, they cut out a 1'x1' piece of sod and dug a hole for five grand. The graveside service was not included in these fee. It was literally just to dig a hole.
There is a mustachian twist though. Her thoroughly charming, but indigent nephew had passed away and been cremated a year or two earlier. He was a world traveler, so his ashes were divided into clamshells and distributed to anyone who was willing to scatter them in the four corners of the world. He and this aunt were fast friends. Someone still had a clamshell, so the decision was made to bury it with my aunt and grandparents. The day after my aunt's service, the family assembled again. We gathered in a tight circle. The flowers were moved, the small square of sod lifted and a small garden trowel brought from home was used to bury the last clamshell. Then we said a few prayers, sang some hymns and enjoyed the fact that the two of them would be thrilled that we got a two-fer of sorts.
Back to my aunt for a moment. When my grandfather purchased the family plot, he knew his youngest daughter was unlikely to wed, so he purchased burial insurance for her. The $5k fee to open the small square more than 50 years later exceeded the original price of the entire plot. Thankfully, the insurance policy just barely covered it.
The point of this tale is that the Mortuary/Funeral/Cemetery Industry is big business and about as un-mustachian as it gets. Advance planning pays off.
To the OP: if your FIL wanted to be buried in the family plot, he had scores of years to make these plans. He did not. It is not your responsibility to do for him what he refused to do for himself. That said, you can be the voice of reason, but you must tread lightly, because he wasn't your dad, deadbeat or otherwise. In the end, it's only money. None of us gets to take it with us.