I never use a square or lineal foot price for anything. It's always based on the particular circumstances for the job, since there can be so many different situations. Generally, for labor costs I'll price by the day, 2 days to do this, 4 days to do that. This will be based on previous experience but I may face specific situations that I haven't done before. I just try to account for all the things that may be part of, or impact what or how I have to do the job. By the foot pricing doesn't account for anything that may be unusual, it assumes that jobsite conditions, sources of supply, installation procedures, materials are all the same.
A while back, I did some staircases that landed on three different balconies. What made the job unusual was that there were two mirrored stairs and the house was a timber frame. Open ceilings, floor joists were 12" x 18" beams. I chose to mount the balcony posts with 2 1/2" round tenons cut into the ends of the posts and sunk into the beams. I think I had to do this to 10 posts. Having to drill large holes in the ends of newel posts along with corresponding holes in the beams added an extra days work. There can be other issues, post to post vs over the post rails, easements, end treatments, turnouts, risers, other rail parts and attachments that vary from job to job. Attaching ballusters can vary from ones that fit in round holes to ones that have fillets between, top and bottom rails to top rail only, one piece rails to built up multi piece assemblies.
250 lineal ft. of rail, posts and ballusters is a large job. If you figured 10 days to do it and it only took you 8, you're making money, if it takes you 12 or more, you aren't doing so well. Pricing at $10/LF is a total of $2500. @ $30/hr. you would have to install 25 LF per day. What's required for installing the materials can vary widely as mentioned above. I think you need to know all the circumstances regarding installation procedures and whether the time frame matches the work load. Since you haven't given any particulars, I'd be a little afraid of that price unless it was very simple. Of course, $10/hr. is a lot better than $0/hr. even though it's not what you may hope or need to make. These days, work is work and a lot of us are underemployed, one way or another. There is a lot more to think about when pricing jobs than just an LF number.