You should never think of your marketing budget in terms of "spend" or set spends each month. Your budget needs to be fluid and based on performance.

If you spend $1 to make $3-$4 then spend until you make less from that dollar.

Competitive insights into marketing spends is tough because no competitor will ever give you access to the real numbers. But SEMrush is probably the best tool in terms of estimating a website's online marketing spend. It only looks at Google organic and paid though, not Facebook or anything else.

I'm happy to run some reports for you on my SEMrush account if you would like. Just ping me.