I would purchase the SSD new, and only if it made sense.
Here is an example laptop that I am looking at. The Dell Latitude E6410 with the Core i5 option. The "primary storage" options are as follows (as of today):
250gb 7200rpm HD (Selected)
320gb HD (+$30)
500gb HD (+$130)
250gb Encrypted HD (+$120)
128gb "Dell Mobility" SSD (+$300)
256gb "Dell Mobility" SSD (+$850)
128gb Encrypted "Dell Mobility" SSD (+$350)
I wonder what the true hardware of the Dell SSD options are, but I am sure that popular third party choices are comparable in performance. The 128gb drive makes a little less sense to go to an external vendor, but the 256gb seems to have a large premium. There are many options on NewEgg that fall well under that price point and support TRIM and maintain high or fairly high speeds.
An example of a 256gb drive:
http://www.newegg.com/Product/Produc...82E16820139114
The 128gb version doesn't make as much sense:
http://www.newegg.com/Product/Produc...82E16820139113
There are a few other benefits to going this route that have much less weight. Mainly I get to purchase a drive that I like from a manufacturer that I trust and research. But also I have a 250gb "backup" drive if ever needed.