I completed an epic job myself, on a semi D, you could hear the neighbours in their ensuite, hear their text pings etc.. after many years and tenants there, it was time to sort it! estimate of cost including a bit of help with the labour and carrying up the sheets of plasterboard around a grand for one room. Rock solid job!!! 1m X 1m squares of italian made soundproofing tiles, and a triple layer of plasterboard - acoustic (really dense), then regular 12mm, then a final layer of acoustic. Very important to vary the layers *as it deters the soundwaves that bit more), stagger the joints too. Plenty of tubes of acoustic sealant and any gap no matter how tiny was filled. massive gaps in the corners, easily 2 inch gaps where plasterboard was not meeting, sloppy work, these gaps let in huge sound too, but notwithstanding that having a few sheets of ply, some insulation and one standard sheet of plasterboard on either house does not make for any level of sound prevention. Super job, happy to email photos. We only did one room, if I still lived there I'd do the whole lot - well worth it for sleep and just general peace. One thing we didn't tackle was the floor, this can be another big source of soundwaves entering, took a chance on this and it was ok. Skim coat, fresh paint, carpet trimmed back and new skirting all done, 2 days total. loss of approx 5 inches floor width. small sacrafice. Builders only now really starting to take sound proofing into consideration - unless it's a private build and this is a specific ask, there is a huge array of materials for walls, floors etc. Acoustic glazing also helped us, fractionally but again worth the install. Was in the house recently, new people bought next door, lots of clattering late at night downstairs as they're doing work, would defo ask them to go half if too was living there. Money well spent.