Hi bro/sis,
technically speaking, Seachem Excel is not a fert (at least to me) but more of a carbon supplement to the plants. It's useful as it provides the plants with the needed carbon (dioxide) plants require to take in to photosynthesize & thus grow. It's very commonly available in most LFSs here, you may wish to scout around for other pricing if time permits (By the way, the $14 is for the 250ml one?)
As for ferts for plants (to make plants grow faster & lusher), Seachem also have one [Seachem Flourish - something like an all-in-one kind...] quite popular among hobbyists. Other brands include Wondergrow, Ferka, Azoo etc... Each got its own +s & -s, you really need to read up more to see which one suits you (or at least the plants you intend to buy for your tank in the future) better... [Better to spend more time to read up & plan ahead before you dive into this hobby than to spend $$ unnecessarily...]
Then there are others (like trace elements, Iron supplement etc) which you may need/want to buy... again, mostly depends on the types of plants you intend to keep...
Hope the above helps...
Cheers!
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