One band, it's fairly easy, you can get P25, DMR and NXDN in a single band radio for ~$1200 or so.
You can only program in 2 digital modes at a time.
If you want a multiband radio, it does get expensive, and there isn't one solution that will do everything, yet.
The EFJ/Kenwood VP8000 currently only does analog and P25 (phase 1 and 2). In the near future, you'll be able to add DMR. Rumors of adding NXDN in the future. You are probably looking at close to $7K
Tait makes a multiband radio that will do P25 and DMR.
For ham use, all you'd be able to utilize on these radios is VHF and UHF. No amateur allocations in the 700/800MHz band.
Other concern, the LMR radios are limited to narrow band on VHF and UHF, so you need to pay close attention. Most radios can have wide band opened back up for analog use, but there's some extra steps involved. Kenwood and Harris are pretty good about leaving the 2 meter band capable of wide band. 70cm amateur radio band is a secondary allocation in the band, so you will need to request wide band for UHF.
Make sure you consider the -entire- cost of ownership. Programming software and cables can be expensive. Accessories are higher priced than the amateur stuff.
Programming software has a steep learning curve.