An outside the family consultant may bring a different prospective of your space. Fees for some scopes of residential design are lower these days. Maybe have a plan for changes now and for future additions.

I would recommend calling around and getting some free estimates. It really depends on what you want (just a plan or someone to make the plan and execute it). We received a quote from an architect in Virginia for $2k (computer plans only) and we would execute the plans. It's nice to get a professional's opinion. PS I love that tree and the tree house!

I think your budget is realistic but it can depend on where you are located and what your vision is for your yard. Beautiful tree, btw. When we did some landscaping a few years back, I got three estimates and picked one. He happened to be the highest but had much more to offer. I also incorporated some of the other landscaper's ideas into ours. Your local nursery can also offer great advice as well.

Many landscape gardeners and architects will give you a planting plan and rough layout for a small fee. If you explain upfront you only want to pay x amount they can tell you what they will do for you.

Try looking for design /build companies in your area. They may offer a more inexpensive option because they will be installing it. Landscape designers and architects are usually a little more expensive (though also more creative).

My feeling is that if the project is worth doing, it is worth planning. A good designer will make the finished product so much better - even if all they do is provide you with a schematic design. Talk to a few whose work you like, give them your budget and scope, and ask them what they can do for you.