Dutchman, for 3D imaging, I think Pro Landscape is the best and easiest to use. It has a lot of plants, but the picture is more important than the actual plant. If a Steeds holly image looks better on your 3D image than the image for a San Jose that your actually installing, than I use it, because the plant list and plan have the correct information on them. It's just a representation of what you are going to do. Some of the photos are great, others are not. Some plants don't have the form you are looking for, but a similar plant may. With Pro Landscape you can also import your own pictures and pictures from the the plant encyclopedia software, Horticopia. Horticopia also allows you to create slide shows, print picture and or data for all the plants you have selected for your designs. They also offer excellent photos, data and formats for presentation. Right now I think my version has almost 8700 plants with pictures and data. You can order additional portfolios that have more pictures of some plants already in your library and other cultivars and varieties. As of now, there is no data in additional portfolios, just pictures.
I understand your concern with costs, but hopefully with the right presentation tools you will sell more and better jobs that will offset your investment. Does the designer work for you or are they an independent. If they are your responsibility the right software will benefit you, but may take longer to recuperate. If they are an independent, they should realize the benefits of the right tools and be able to service all their clients, including you, better.