Once you research the cost of acquiring negative carriers and, to a somewhat lesser extent, lensboards, you'll see that they significantly effects the total cost.

But I'd go first for the 4x5. You can buy a 2nd carrier and a 50/2.8 Nikkor and still be under $100 (if you shop carefully). Note that it is missing the baseboard.

If space is an issue, given that you don't plan to do 4x5, and assuming the seller is flexible on price, I'd go for the 23C. I'd offer no more than $100.

If you need the timer, etc that is with the c700, make the seller an offer for everything but the enlarger.

My 2 cents.