my thoughts, for what it is worth, is keep your existing soil (unless it is really bad stuff). If it has worked well up to now keep it. It is accustomed to your back yard and if it is reasonably fertile why spend money replacing something that is useful.
Whether you need to till the rest of the sand in to the soil or add some extra soil or organic matter to create new levels you have not said but what you have is likely to be best for your garden.
If the soil is quite sandy already you may turn over some compost in to the soil along with any remaining sand to create a decent soil mix. If you bring in new soil you can also bring in new seed and weeds.
Whether you level and reseed or sod is another choice, I myself prefer seeding. Sod seems like sodding hard work.
rob