Sikkens recoating?

The records I inherited from the prior owner of my house show that the cedar deck was coated when built in 2008 with Sikkens SRD 077 stain. The deck is 300 sqft desk; it has a 100 sqft steps/railing. The deck and steps require recoating as the original stain is worn out in many places (no peeling). The railings look OK. Unfortunately I am in no position to do the job myself. I got some proposals and the quotes vary so much for the same job (with the same assumptions) that I am confused.

Each proposal shows two options:

a. Clean the deck, railings, steps with Trisodium Phosphate or sodium per carbonate and then recoat them with what was used initially (Sikkens SRD 077 stain); no power washer to be used. The quotes range from $400 to $1,000 including the stain.
OR
b. Sand everything (no stripping and brightening) and stain it again. The quotes range from $850 to $2,500, including the stain (assuming SRD).

These figures seem astronomical for the above mentioned size (comments from neighbors). Based on your industry experience what's a "reasonable" range for the charge for this job?

Thanks in advance for your help.