I agree that you need to spend the money and do it. If I were looking for a 500k house, I would be very put-off by the lack of outdoor space. In regards to furniture, set up a price alert from Amazon or whoever, and buy patio furniture this winter, when they are clearing out all the previous season left overs. We got an insanely good deal on a very nice set, reduced in price by 70%. If you only have a small space, you might get remnant stone for a good price. You also might be able to save money by doing the work in the winter.
For the base, I know nothing about how to resolve drainage issues, but you might consider asking if they can do it with Item 4, builders sand, and pavers. We installed a patio near the pool and wanted it to look natural. We didn’t want a concrete base or anything that was going to crack and shift in the winter. We put top soil between the stone pavers (irregular shaped) and seeded it with grass. It’s no maintenance (except for strimming) and looks good.