according to my calculations, from the December 2013 issue of QST magazine, 10W of CW is equal to ~500W of SSB. PSK is even better than CW.
check my old thread here, which references the article, so you can read it yourself. makes for interesting reading/thought-provoking:
old thread i made
ETA: most of the replies in the thread linked didn't do the calcs, unfortunately. "robmkivseries70" seemed to have seen the dB figure i quoted, & one other poster "wdlsguy" seemed to go a calc that got him 10W CW = 270W SSB.
take a look & see what you think. of course,
ceteris parabis, you are always better off w/ more power, for a given mode, but if you are willing to trade CW skill for $$, it seems like possibly a reasonable way to go, while saving up money for an amp or a full-strength xceiver.