The first thing I ask about is whether a car ever rolls across the walk, because that part needs to be built stronger and I want it in the estimate from the start. On the job, our crew breaks out the old walk and hauls it away, then digs past the topsoil to firm ground, since anything soft left under there keeps settling after we leave. We pack the subgrade, the ground the slab sits on, and keep it even where the walk crosses a utility line or meets the driveway. We set the forms with a slight fall away from your house so rain runs off instead of back toward the foundation, and where a car crosses we thicken the slab and add rebar, steel bars that hold the concrete together if it cracks. We like to pour in the cooler part of the day, because concrete that dries too fast in midday heat can end up with a weak, dusty top. Then we give it a broom finish, a light texture dragged across the surface so shoes grip when it's wet, and cut control joints, shallow grooves that give the slab a straight line to crack along. Concrete does crack, so the goal is that it cracks in the joints, where you'll hardly notice. If you have to trim the budget somewhere, I'd rather you skip a fancy finish than a proper base, because nobody sees the base on day one but it decides how the walk holds up.
Sidewalks are flatwork, the same family of flat slabs as driveways, patios and garage floors, so a walk is often one piece of a bigger job. If your walk runs up to the garage and the floor in there is cracked or sinking, we can price garage floor concrete on the same visit. If you want the walk to look like more than plain gray, with a colored border or a pattern, that's decorative concrete, and it goes over the same packed base.
Plain broom-finish walk
This suits most front walks and side paths, because the broom texture grips in rain and slush and it's the simplest surface to shovel and keep clean. It also puts most of your money into the base rather than the top, which is where I'd want it.
Walk with a driveway crossing
This is for any walk a car or truck rolls over, where we build that section thicker and reinforce it so the weight doesn't break it up. Mention those crossings when you call so they're priced in from the first estimate, not added later.