Is your drainage up to scratch? If there is gravel drains installed mole draining will help if not it won’t. I’ve never felt it nessasary to subsoil a good grass ley should self structure through roots and wormsHeavy clay soils what's the best routine to keep soils well aerated and to keep the drainage tip top.
My neighbour bought a opico swardlift and I got him to do two half fields 2 years ago no noticeable difference waste of time in my opinionA spade. Dig a hole and see if there is a problem and, if there is, at what depth.
I expect there are plenty of secondhand grassland subsoilers and aerators available that have seen little use.