You may be able to get a 2nd or 3rd year apprentice to wire your house for considerably less than a RECI registered sparks, then he can have the installation tested and certified by a RECI installer- this is done routinely and is perfectly above board as the installation is tested and no one will put their name to a dangerous or poor installation. Just another option.
Doing the first fix (chasing walls, notching/ blocking out stud walls, fitting galv. boxes etc) is still a DIY option but the wiring of the accessories is not.