For that price you are not talking about a new laptop. New laptops with an upgradable (socketed) CPU start at about $1200. You can get a used one for less, but for that kind of money you are talking about a much older laptop. The most easy to find laptop that can have the CPU upgraded (USA market) is the Dell Inspiron 1545. For $230 you can get a system with a Pentium dual core CPU, 2 - 4GB of memory, and a 250GB drive.
You are probably better off going with a new economy laptop from Dell or HP. For $300 - $350 (when they are on a sale) you can get a system with a current i3 CPU, 4 GB of memory, and a 500 GB drive. The i3 CPU is the only part I would look out for, as it costs about another $50 to get over the Pentium and Celeron models - and makes the laptop much faster. The hard drive and memory can be upgraded. The CPU can not on value units. The socket that allows the CPU to be replaced or upgraded costs money, and the manufacturers want to save money.
I usually keep an eye out at
http/techbargains.com to see what is on sale. They are a dependable site with good information and discount codes. Watch out for those pricing error entries that occasionally go up, though. Those ones say something like "supposed to take $xx off, but actually takes $xxx off". Those ones are valid, but the manufacturer may want to "correct the error" and cancel the order or charge the correct amount (to what the coupon code should have made the price go to).
Techbargains currently shows a deal on a new Dell Inspiron 15 3000 laptop (yes all of the numbers and space are part of its name) for $342 with an Intel i3 CPU, 4GB of memory, and a 500GB hard drive. It does require following a link from:
http/www.techbargains.com/jump.cfm?clkSubId=BD444474ZZ0A00444474C84&afsrc=1&id=9700&tb_arg_id=65114
and entering this coupon code on checkout:
?4ZG11G3WRVBT3
Hopefully I have helped you. Good luck!