Some free alternatives to AOPS:

Hoagie's list some free online courses - http://www.hoagiesgifted.org/online_hs.htm

OER Commons (www.oercommons.org); Curriki (www.curriki.org); www.goodsitesforkids.org have materials, including courses, as well. E-Learning For Kids (http://www.e-learningforkids.org/) has interactive games up to 6th grade, but there are others on the Good Sites for Kids. Might also check out resources from www.livebinders.com - under subject, grade/age, or using search engine (i.e. entering gifted as a term).

There's tons of free OER (open educational resources) today; no need to shell out money and deal with the repetition and/or rote learning. Create/design your own.