Comparable, well, that depends:
Are you using the NexEdge digital emissions on that radio, or just the analog?
If you are using NexEdge digital, then you MIGHT be able to use an Icom UHF IDAS radio. NexEdge and IDAS are basically the same, it's the NXDN protocol that was originally developed by Icom and Kenwood. The big difference is that Kenwood lets you use NexEdge in 12.5KHz (narrow) or 6.25KHz (very narrow) mode. Icom only lets you use it in 6.25MHz.
If they are using trunking, then you'd have to stay with Kenwood. The Kenwood trunking protocol is not compatible with the Icom trunking protocol.
If you are just using the analog function of the NX-300, then any narrow band capable UHF analog radio will work, doesn't matter who the manufacturer is. Motorola makes a few compatible radios, so would Harris. Likely Harris doesn't make anything comparable in price. Harris tends to be high end stuff. Motorola would likely be more affordable. You could also look at Icom, Vertex, EF Johnson, Datron, etc.
If you are just comparing systems, then NexEdge digital is comparable to the Motorola MotoTrbo on a marketing level, however they are in no way compatible in digital mode. Analog they would work together just fine.