Each Appian exam attempt runs $250 now, and each level- Associate Developer, Senior Developer, Lead Developer, and the separate Analyst track- is its own $250 fee. So if you go the full developer path from Associate through Lead, you are looking at around $750 total just in exam fees, and that is before you factor in any retakes if you fail an attempt. Appian partners get a 50 percent discount on that, but only if you are working through a partner organization's account.
There is no bundled "program price" that covers all levels together; each exam is booked and paid separately when you are ready. Study materials and Appian's free Community Edition environment do not cost anything extra, so your real spend is mostly exam fees plus your time. If you want practice resources to gauge readiness before booking, CertBoosters has some for the ACD101, ACD200, ACD301 and ACA100 exams: www.certboosters.com/appian/path/appian-certification-program