If the house is so old as to not already have a receptacle under the sink---pre-60's construction locally---the electrical costs will be high due to having to add the receptacle. However, if there is a counter receptacle above where the proposed location, adding a receptacle is fairly easy. I have done an installation like that by dropping the wiring straight down behind the new opening and using surface conduit to run laterally to the sink area and installing the new receptacle---took less than an hour.

The actual carpentry cost will vary---depending on the cabinet construction and what needs to be removed and how easy that removal is.

Plumbing consists of attaching the discharge line to the sink drain or the garbage disposer. Water supply is done by adding a T fitting and a shutoff.

I can't remember what I charged the customer---but it was less than $400 for parts and labor---including installing the DW.

One other consideration is the depth of your counters. Many older homes had kitchen base cabinets that were less than 24" deep. If your cabinets are less than 24" deep, a dishwasher won't fit.

If a built-in doesn't work for you, then a portable is certainly better than no dishwasher at all. You'll just need to run it during periods when you're not needing to use the kitchen sink.

If you've never had a dishwasher, one of the greatest things about them, isn't that it washes the dishes (which is a very good thing), but that you can get dirty dishes stashed somewhere, out of the way, until you're ready to wash them. A portable does that as well as built-in.

James