For simplicity & cost I’d go with Neil Thomas’ “Ancient & Medieval Wargaming”, using a mixture of Hat & Zvezda 1/72 figures.
I’ve played a lot of games in your target area (see these posts: http://wargaming4grownups.blogspot.co.uk/search/label/Ancient%20%26%20Medieval%20Wargaming), and they play really well. Everyone claims their rules are “fun” and “easy to learn” and mostly that’s because they’ve grown up with them. Hail Caesar may be great, but the rules are buried in a 200 page book. The AMW rules cover about 4 sides of A4 max and are learnt in 10 minutes. Honest. Sure there are holes in them but the system is easy to tweak and if you’re playing with friends it isn’t an issue.
The figures are based on standard element sizes so shifting to other rule sets is fairly easy.