Those are both perfect, but each is actually two sentences. You need to put a period after "busses". You shouldn't use a comma to separate two sentences. Here are some other ways: "I'll be coming over on foot 'cause there aren't any busses." "There's no bus to take so I'm walking over." "With no busses, it looks like I'll be strollin' on over." There must be hundreds of ways to say this. Notice that most of my solutions, just like Dan's, use present participles. They work very well in friendly conversation because they are descriptive and flexible, the opposite of scientific or precise. Notice also that you don't need to use the word "will". It does no harm. You can use "will" if you want, but it is not necessary for speaking about the future. Your phrases "I will come" and "I will walk" are perfectly fine, but they don't feel as relaxed as phrases that use participles.

Hey Franny, I just realised there's no buses going from my place to yours, so I'm walking instead - might take a bit longer, but I'm still coming - see you soon... Okay, bye!