... they're kinda' pricey...  ...

Why not?...lol
Even them lil gel inserts are like 60 and 80 bucks. Id like to find one CHEAP to try out in mine. Modded the seat a lil with a lift but the foam is still an arse killer after a 150 miles.
Even thought of trying some of that exercise pad foam some have mentioned.

Just in case this is turning serious...

I just bought this
http://www.walmart.com/ip/Coleman-ATV-Comfort-Ride-Seat-Protector/16777864  $17

It is a very good fit on a stock 1 piece saddle, maybe an inch or two short in the back.  I hacked up a one piece to make a low profile seat a while ago.  Recently bought this and stuck it on the smoothed out seat pan with the vinyl over it.  So for so good.

(Not an original find by me.  Some advrider forum folks swear by it for long rides)

I spent a lot of time and money making my S50 more highway worthy (forward controls, bigger windshield) this spring thinking I'd test it out going to Laconia, about 120 miles to the site we camped at.  At the last minute my daughter and her boyfriend decided to come so he rode the S50 (loved it) and I rode the mini-bagger/cafe/bobber with it's custom seat.
By the time I got there (well before, actually) my butt was SORE!.  Since I had to ride back the next day I found a vendor selling sheepskin covered foam/gel pads and spent $90 on one.  It was worth it on the way home.  Much more pleasant trip.  Along with extra softness it raises me up at least an inch for better ergonomics too.  You can see it in this pic from the return trip.
It's very easy to install and remove so I can use it just when I want and on either bike.

SuperSavage wrote on 06/29/11 at 14:24:58:

I used 1 1/2" memory foam inside on top of the original foam. Two years, no issues.