pricing

perhaps $40-50? it's really hard to say.

using (2) 21" mowers doesn't really fit the mold for $1/min that some guys use.

until you get the commercial equipment i don't think you can justify the commercial price.

just using 21" is not going to be justifiable to the home owner that you are charging them $50 to do their lawn in an hour, where as other companies may charge $25+ and do it in a fraction of the hour.

You do have to start somewhere

If the going rate is say $25 to do a lawn, then why not try for that price or a couple dollars less. Don't cheat yourself and do it for $16 - $20

i started that way 15 years ago good luck
try to find out what the other lawns on that block are paying?
get as much as you can, you do not want to be the cheap guy you want to be the quality guy, try renting a walk behind one day and see if that helps many rental places now carry them
bottom line do not do it for free

Do a search on price and you should get lots of threads to read.

I remember a long thread asking what people charge per yard and I think most said minimum $25 yard which I assume is for a typical suburban yard with average size yard (under 1/4 acre).
Just depends on what going rate is in your area.

It will probably take you an hour+ for mow/trim/blow with a 21" vs. 1/2 hour+- with 36" or greater walk behind.