1st, you can cut costs alot by adding mostly dry sand, my reccomendation is aragonite, if you can get some, and if not silica and quaartz sands have been rumored to be a not so good thing, but lately it seemsthat hte rumors were just rumors, i know of a lot of people who used quickrete sand(which is quartz), and silica sands, but my first choice is still aragonite, it is a better substrate to use for aquariums, and only add one bag of ls, the ls will seed your dry sand, adn if you have lr, that will also seeed your sand bed, but you are probably looking at aaround the estimated figure
2d, i won;t use any rock in mya quariums, except for either live rock, or if i must cut cost, i will use tufa(which is reef rock from under the reef) rock(you can often find this at landscaping supplie stores, for @ 1$/lb), some may say they used limestone, but i will not, personally
and last, you should cycle the tank until it is finished, there is no way of telling how long, all systems are different, and to say one month or 2 months, may not be accurate, it can take anywhere up to a couple of months, depending on how much lr, if it is cured, how much ls you use in your mix, all factors can change things, but how you tell is by watching your ammonia levels, it will rise, then fall(on it's own, do NOT try to lower it in anyway), then your nitrites will spike and fall, and your nitrates, after your ammonia and nitrItes peak and reach ZERO, then you can do a small water change and start adding fish(i would wait one more week, to make sure that it stays stable at 0
<a href="http://home.gardenet.co.za/landman/Starting%20with%20Marines.htm" target="_blank">read this article, it will help with some info and cycling questions</a>
HTH,a nd come back and ask more questions