I bought my B2910 used with 300 hrs and mmm for $9900. The B2910 is an awesome tractor. it was top of the line in it's day. Every comfort feature you can imagine
I looked at a 3700 for about a minute on a dealer's lot and realized it is a very basic tractor.
So I don't think your original comparison is very accurate. To compare features you'd have jump to the 3030.
Good luck with your shopping. Keep in mind, always compare tractor features when comparing different models/prices.
I attached a couple pics to show size comparison of the B2910 to a JD455. I loved my 2910. When I bought back I went bigger and gave up mowing.