I would say yes, if the plant is something you can't find at a local nursery. My experience is that mail order nurseries double or even go higher than what you can buy from a local nursery. Then they charge very high shipping prices, even for one plant. My experience is if a plant cost $3 to $6 at a local nursery, expect to pay $6, $12, $24, or higher at a mail order site. Then they charge $10, $24, or higher for shipping. I try to limit my online shopping to only plants I can't find at local nurseries because of this.

I've purchased Mountain-ashes from ForestFarm. The shipping isn't cheap, but they pack them well and they arrive in great shape.

Considering the PNW is one of largest commercial plant growing areas in the country and most local garden centers are very well stocked, NOT being able to locate something easily often has a very good reason behind it. The problem with buying online is that it won't have that sort of location appropriate filter applied to it.

Crape myrtles are just not great plants for this area. It seldom gets hot enough in summer for any length of time to encourage them to bloom. The large display planting in the parking islands of the Center for Urban Horticulture has pretty much bit the dust and that planting site was considered more or less ideal - open, full sun and lots of reflected heat. If you can replicate that sort of environment, especially the reflected heat, you may have some luck but crapes would never be at the top of my preferred plant list for the maritime Northwest.

I've mail ordered many plants, it is worth it if you can't find it locally.