Call me old fashion but can't you do that by simply counting how many hours you see each phase of the job taking you then measuring and counting all supplies needed. And then add them all together allot of the materials we use can be memorized rather easy. For instance I know a yard of top soil delivered from my guy costs 25 per yard sometimes a little less so I go with the 25 figure and add on a price to spread each yard. Mulch is also simple dark premium is around 25 a yard here cedar is 30 red cedar is 35 so figuring an estimate is very easy once you know your prices.
Something I do is count the hours in my head how long will it take me to do something If say its a brush job I may add and hour every few feet perhaps 100-500 sq ft all depends what your doing I then add the hours and times my price which is usually 30-35 and hour. But that price is what I think the job will be if everything went wrong I happen to like my toys and invest a lot in having equipment that can speed up my process. So when all is said and done the real rate may be 50-100 an hour.
The plant material or other hardscaping items like pavers and such you should be able to get the prices from your suppliers price list book I prefer to use the most expensive suppliers prices I have so in case I have to buy from him I am covered I guess what I am telling you is estimating is more by feel then it is by a ridged price system. It is rather fun once you get good at it I probably will be meeting 250 different clients this year and you never know what is going to answer the door.
I purchased a very good manual off the PLCAA website from Nilson. It gives industry standard work measurement for just about all landscape and maintenance jobs. It gave me a good idea of how much time to estimate time performing different jobs that I had not done before and did not have hands on experience with. It has tons of useful information.