The 3 bolt thing sounds like your crank is one of those cheap steel cranks with the inner ring removed.A large quality cog(like EAI)is going to cost about $30.For $10 more you could get a bulletproof crank.Those are decent low end cranks and usually come with a 48T.If that is still too big,you can easily find cheap 110 chainrings.I think i payed $9 for a 44T @ the Lbs.