Book cover: many use templates available for free with some retailers; upload their own photos and choose font type and style and are done with it. Super easy and free. But what if you’d rather want a professional cover designed by an expert to stand out from the crowd? I would say the price for a full cover (front/back/spine) from a good designer will vary drastically but target $200 to $500.
Layout/typesetting: some use free online conversion sites (not recommended) or the retailers’ own online conversion process. This is both problematic and can result in many issues or at least some poor layout/typesetting which will lower the reading experience. Want to have it done by professionals (and get all files required to upload to ALL major retailers)? Pricing varies greatly again, but take $200-$500 as ballpoint figure.
Editing: the most costly part of all. Many shy away from this due to cost. If you are confident in your writing, you can maybe get away with a simple copy-editing ($50 to $100+ per 10k words) just checking for spelling mistakes and grammatical errors and skip full line editing ($80 to $200+ per 10k words).
Book uploading to retailers: Free; do it yourself – you do NOT need to use third party aggregators/distributors – every major retailer allows individual accounts to self-publish.