Machetes are not something that typically need a perfect edge, especially if you're dealing with soft 1075 steel that is not going to hold an edge very long.
I think a ballpark estimate would be a dollar an inch for sharpening.
You might want to look at a Worksharp belt grinder. They're relatively cheap and easy to use. They will put a convex edge on your blade; how convex an edge depends on belt tension where the edge meets the belt and the pressure you apply.
You might want to consider that the term "convex edge," by itself, means almost nothing in practical terms. A convex edge could be nearly identical to a V edge, or quite a bit different. It could be very obtuse or very acute or somewhere in-between.
I had a well-known professional knife maker offer to put a convex edge on my 3V parang -- convex meaning he used a belt grinder. The edge turned out beautifully and has lasted a long time. I've also gotten a custom knife from a maker who put a horrible convex edge on his knife. The knife was barely useable. I think you'd be better off looking for someone with excellent skills who will match the edge he puts on your machete to the type of use you give that machete.
But in the end, you'd be better off with a Workshop and learn to do it yourself, experimenting with more or less obtuse convex edges.