Why the obsession with saving money? How about you get a waitrose card and go and queue for a free coffee instore?
Or how about spending the money and enjoying good coffee at home? Which if you want an espresso then neither a stovetop or aeropress will make one.
A gaggia classic is the stock answer because they are very good for the money with proven internals and a commercial grade chromed brass group head and portafilter. Spares and mods are freely available as they have been popular for a very long time and a proven design.
You say you have a grinder but if it’s a blade grinder not a burr grinder it will be useless for espresso so you may have to rethink that.