"Why are tabletops so expensive?"
Primarily because there's not much profit in selling a slab of plain-Jane MDF. Dress it up, fit it out with grooves, slots, clamps, edging, make it out of cast iron, expensive plastic or unobtainium, all ways to jack the price and up the profit margin.
My first router table was a piece of cabinet-grade birch ply underpinned with a frame of 5/4 quartersawn heart pine, all salvaged from job site leftovers. Routed a 1/4" recess to fit my two(yes, just two) router bases, drilled some holes for screws and I was done. Worked fine for me for over fifteen years. No base, it just hung between two sawhorses.
I succumbed to the hype, made my new table top out of laminated BB ply, slathered it with contact cement, layered on the Formica. Cut a big hole in it, routed out a ledge and hung a Jessem lift in it. Put all this stuff together and guess what? My old piece of birch ply was flatter by a big margin....
I like the lift, love the Incra fence but the top is severely lacking. Yeah, it's pretty and real slick but not flat worth diddley and that's what counts most, right?
My next try will most probably be something like Quillman's table
. KISS principle, sometimes less really is more. Add some reinforcement around the opening for the lift, probably aluminum bars, and I'm there.
Lots of hype in the woodworking equipment business nowadays, folks selling high-$ solutions desperately seeking problems. A healthy dose of skepticism is a good thing if you don't have money to burn, sounds like you've got a head start in that direction. Keep an open mind and a firm grasp on your wallet, you'll be better off.
Great thread! Ducking and covering.......