Grinder pump installation cost?

My house has a large detached garage with a stubbed out sewer line. I am looking to install a grinder pump to connect up to the sewer, as the garage is too low to run a gravity line to the street. I've gotten one bid so far, which was about 6000$ to hook up the grinder and run about 80 feet of pipe out to the sewer line. Does this seem reasonable? One item that I thought was strange is that the contractor said the pump would cost 3-4K, yet I see grinder pumps online for a bit over $1000. Of course I'm going to try to get another bid, but I'm wondering if there is something that I'm missing which would account for the price discrepancy from what I see online with what the contractor said. I'm living in the Seattle area.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.