Looks like it may be a counterfeit, but it is definitely not a Machins. 1775 seems to be the most common year for counterfeit British halfpence.
Yes, period counterfeit, hard to say on value. There are people who avidly collect them and some rarer ones go for better money, but most aren't terribly valuable. You can probably check completed ebay listings for some idea.
This one was on ebay i bid on it and it but lost it sold fro 42 dollars plus shipping last night but still i would like to learn about it so i know better next time !!