I installed mine last spring, and it was MUCH easier than I anticipated. I had three helpers with me; two of them went around digging the trench, I followed laying the wire and the last helped followed me, filling in the trench to cover the wire. We reserved the whole day and were finished in about 3 hours. DEFINITELY worth the savings, IMO!
I like my invisible fence so much, I bought one for my aunt and uncle...THEY had quiet a bit more trouble with installation than I did...my uncle rented a trencher since their yard is much bigger than mine, and then he accidentally cut the cable and phone lines to the house. Needless to say, my aunt was NOT a happy camper about that one. They were without phone/internet/cable for almost a week before the company could make it out to fix it, and of course, they had to pay a fee for that. But they like the invisible fence now that everything's in working order.
Having said that, I'd make sure to know where all of the underground cables are before digging ;)