These machines don't have enough spindle RPM, or rigidity, to really take advantage of carbide. I can pretty much guarantee that HSS tools, properly used, will give you the same, or better, performance than carbide, at about 1/3 the cost. I use nothing but HSS on both my Torus Pro, and my 9x49 knee mill. I've used carbide, but it gained me nothing.
Best thing you can do is buy good, American-made HSS tools, and use a good feeds and speed calculator - like FSWizard or HSMAdvisor (Google them) - to set your feeds and speeds. I've never even seen an NM-145, but I can pretty much guarantee your machine can be probably worked harder than you are working it at present.