full range speaker suggestions

Please define full range. 20Hz > 20KHz? Good luck.

Flat across those numbers is a not so simple move, and then there's the room too. Finding 30 - 35hz is much easier and the choices are far far greater in those products which will then suffice or perform.

...and how much is in the till for the upgrade?

I'd think more about a sub than changing out for fuller range speakers.

True full ranger's on 100wpc tube amps that can provide substantial bass impact and depth as a sub would give is not quite so easy a task IMO.

if in a moderate to small sized room, Sonata IIIs might work for you. Dynaudio Esotar tweeter and bass ddrivers that begin rolling off around 30Hz in a 21 enclosed room.

Several folks in the know have at one point told me to look into the Total Eclipse or Super III with the soft domed tweeter.

your room size is gonna play a big part in this...

Maybe Dunlavy scIII,scIV,scV or scVI would do the job you are looking for;I had scIII's driven by cary slam 100's (90 watts triode) with excellant results.

All of the Dunlavys perform at superlative levels. If your room is large enough the SC-Vs are close to perfection and are truly 'full range'.

though not the final word for deep bass (many of the above mentioned are not as well) your sf's are certainly competitive with just about anything. in fact, they should be the speaker you've described. this sounds like placement, the room, or boredom.