Diame is top class for only 3.5m, Honda is always cheap. He won't give instant impact but Pugliese at Atalanta is amazing once developed and only 650k compensation.
For RB it's a bit trickier as the best ones are generally very expensive, there's plenty of cheap LBs so maybe you could get one of those and re train him for RB?
Out of RBs I'd say Eric Dier is probably your best bet on the cheap, he's natural at CB but accomplished at RB and DM and would provide great cover
For LBs you can retrain, if you want a purely defensive one Jonathan Silva from Estudiantes in Argentina is top class and only around 3 or 4 mill, Federico Alvarez is a bit more attacking but cheaper at only 2 to 3 mill from Belgrano in Argentina and if you can stretch you budget then Nicola Murru from Cagliari in Italy can play both RB and LB very well, shoudl cost around 8mill at the start and is a great young option
Hope that helps