I highly recommend getting into the War of Spanish Succession. You can get the boxes of 36 infantry, or boxes of 12 cavalry, or boxes of 2 cannons w/ crew and bonus 2 officers from Wargames Factory for $20 (or $15 from most online discounters). They come with enough different heads and accessories to be able to make 90% of the French, Dutch, British, etc units that fought. Effectively getting an entire army in plastic.
The infantry are not the best plastics but are dirt cheap and paint up really quickly - for example: