I would agree that learning on a
dinghy or small keelboat, like a Soling, is really the way to go to learn. Learning on a larger multihull can be somewhat more difficult, as there is less feedback, but in many cases, the trimarans handle much better than the monohulls.
As for budget, I would budget $10-15k for the boat, and then use the rest to pay your taxes, insurance, marina fees, repairs/upgrades to the boat, etc.