Hi - My father is a paraplegic and we just remodeled his bathroom last year. We searched online for a long time trying to find a solution that wouldn't cost a mint! We went with the Sterling “Accord” model of low profile shower and surround. We purchased from Lowe’s. It works out well for him as he’s able to get his wheelchair right up to the lip of the base and then transfer to his handicap bench. American Standard does have an option to order a bench with the shower, but we opted for his standard medical grade one that he already had. I want to say that the lip on the base is about 4” tall. Cost was around $750. Sterling also makes several models that are ADA compliant, however they cost lots more.

Here's a link to their website
http://www.sterlingplumbing.com/baths-and-showers/shower-stalls/Accord-R-Shower-72270100-detail?productNumber=72270100&resultId=1854131872-0