When I turn the key I hear a rapid ticking but the engine isn't turning over. The ticking/clacking is rather noisy.

Lights and everything come on. Seems to be plenty of juice.

For about a week up until today, it had been dragging while it was being started. Come this morning and now all I hear is the clicking.

If it's a starter problem, is it a part that can be replaced individually such as brushes/contacts? On a very fixed budget but need to get my truck working again.

Thank you in advanced.

It's probably either your battery is dead or your terminals are making a bad connection. Your lights don't use much current and will usually seem ok. Your starter uses alot of current and will show up a weak battery every time.

Definitely battery.