Repair or replace your stamped concrete
When a stamped slab is sound but the color has gone flat, it usually needs a good cleaning and a fresh coat of sealer, not new concrete. Cracks that run through the slab, sections that have sunk or water that pools are a different matter, because they point to a problem in the base. A new surface on top won't fix that, so in those cases we'd take the slab out, rebuild what's underneath and pour again.
What shapes the cost of stamped concrete
Size and pattern set the starting point, since a detailed pattern with several colors takes more hands and more time than a single texture. Tearing out an old slab and building a proper base add to the job, and the base is what people most want to trim because nobody sees it on day one. If something has to give, please cut a color or simplify the pattern before the base, because a handsome surface on a weak base tends to settle and crack.