You cannot.
The shop offer last week was an error on EA/PopCap's release, there has not been anywhere in the design to allow a player to buy one specific plant seed over and over again.
The fault has been fixed on last data push and the shop offer has now been considered to be correct.
EDIT. I am still kicking myself because I did once have an offer of Bowling Bulb seeds on this offer and missed my chance to have a first M200 plant. ☹️
147M is a very large amount. But this limitation to only spend 21k a day is the clippling factor. It will take near two decades to spend that 147M.
Personally, i never intended to level all plants. Just a few of my choice and ignore the rest.
@af9j7yzxeuor Coins are very useful when you have entered the realm of mastery.
Even for a single plant, it requires 972000 coins to go from M1 to M200, whereas the amount of seed packages required is 30K.
If you are interested to find out more, the details are listed in Fandom.
