HI, yep rover colt, Early to mid 70's going by the blue wheels and red seat. Unfortunately has a later model engine on it, colts only had white briggs 5hp's (major) and red 4hp's (minor). Briggs went black in the 1980's. I can also see some sort of hitch mounted to the front that is not original, if it has been used to move trailers I would not have high hopes for the gearbox condition.
In saying that, Finding red seats in that condition is very hard these days, that would clean up very well
Ultimately it is worth what someone is willing to pay, I have seen good condition running colts sell for $300+, personally I paid $30 for mine, all it had was a stuck valve.