Replacement Torsion axle needed

So my 10 year old Ameratrail Trailer torsion axle is worn out. (It stays fully compressed). So im looking to get a new axle but im unsure what # rating I need.

The boat is a 18 sterling(1000#)
motor is a 90 yamaha 2 stroke (270#)
35 gallons gas (~270ish)
T motor and 3 batteries (215#)
plus gear (~150#)
trailer weight(400#)
total -2305#

The trailer says it is rated for 2900#'s but im guessing the axle has to be rated for more to absorb bumps etc.
There is a 3750# axle for sale on the sportsman for $250 which looks like a deal to me.

What size axle do i need?
is $250 a good deal on an almost new axle
Where would have the best prices for this?