What kind of tools, if any, do you already have? What's your budget? Where are you located?
You can often find a usable 4.5" angle grinder at your big box stores for around $20 to $30 dollars. Use a bench vise, or even just a c-clamp on a workbench, sawhorse, or a table of somekind to hold the blade while you cut it.
Another option is drilling holes around the perimeter of the blade profile and "connecting the dots" with a hacksaw. You might also check your local craigslist or other classifieds for a used porta-band, or even a vertical/horizontal band saw.