One big thing:
Johnny Jump Up - $19.50 Amazon.com
Playskool Weeble 2 pack - $5.00 Walmart.com
Learning Curve First Keys or Sassy Ring-o-Links - $2.99 Amazon.com
Fisher Price Rock-a-Stack - $5.95 babyearth.com
Classic Rubber Duck 3 pack - $4.99 Amazon.com
This is what I have so far and it's under $50 which is not bad at all. I know that relatives will buy him clothes and stuff. Some other suggestions for babies in the 5-7 month range are..
Soft blocks or balls
Jumparoo (on the pricier side)
Bath Sqirty toys
CLOTHES! - they aways need clothes
A tip for mom's buy used toys-make sure you wash thoroughly and spray with clorox. I scrub mine and put them in the dishwasher on steam clean. Used toys are excellent as long as they are NOT used stuffed animals or plush toys-they contain icky things.
P.S. Walmart.com has a section under baby toys called "toys under $10"