I would look at some of the CCIE workbooks from well known provider like INE or IPExpert and see what hardware they are using in their topology and just buy a subset of those for your CCNA/CCNP study.
If you have limited budget, you can start with Cisco 3550 Enhance (non-XL) which is older but a lot cheaper, although keep in mind that 3550 is considered obsolete for CCIE study. If you can spend more, definitely get the original 3560 or better. If you can find a 3750 with comparable price as 3560, then 3750 is even better. Do not get any 29xx switches as those are only L2 and cannot do dynamic routing and other advance features.